Parkinson’s disease (PD) is a progressive neurodegenerative disorder that is characterized by the loss of dopamine neurons in the substantia nigra pars compacta, culminating in severe motor symptoms, including: resting tremor, rigidity, bradykinesia, and postural instability. In addition to motor deficits, there are a variety of non-motor symptoms associated with PD. These symptoms generally precede the onset of motor symptoms, sometimes by years, and include anosmia, problems with gastrointestinal motility, sleep disturbances, sympathetic denervation, anxiety, and depression. Previously, we have shown that mice with a 95% genetic reduction in vesicular monoamine transporter expression (VMAT2-deficient, VMAT2 LO) display progressive loss of striatal dopamine, L-DOPA responsive motor deficits, α-synuclein accumulation, and nigral dopaminergic cell loss. We hypothesized that since these animals exhibit deficits in other monoamine systems (norepinephrine, serotonin), which are known to regulate some of these behaviors that the VMAT2-deficient mice may display some of the non-motor symptoms associated with PD. Here we report that the VMAT2-deficient mice demonstrate progressive deficits in olfactory discrimination, delayed gastric emptying, altered sleep latency, anxiety-like behavior, and age-dependent depressive behavior. These results suggest that the VMAT2-deficient mice may be a useful model of the non-motor symptoms of PD. Furthermore, monoamine dysfunction may contribute to many of the non-motor symptoms of PD and interventions aimed at restoring monoamine function may be beneficial in treating the disease.
VMAT2; dopamine; norepinephrine; serotonin; depression; olfaction
Loss of dopaminergic neurons in the substantia nigra pars compacta and the resulting decrease in striatal dopamine levels are the hallmarks of Parkinson’s disease. Tgfβ and Gdnf have been identified as neurotrophic factors for dopaminergic midbrain neurons in vivo and in vitro. Haploinsufficiency for either Tgfβ or Gdnf led to dopaminergic deficits. In this study we therefore analyzed the nigrostriatal system of aged Tgfβ2+/−/Gdnf+/− double-heterozygous mice. Unexpectedly, we found no morphological changes in the nigrostriatal system as compared with age-matched wild-type mice. There were no significant differences in the number of TH-positive midbrain neurons and no changes in the optical density of TH immunoreactivity in striata of Tgfβ2+/−/Gdnf+/− double-heterozygous mice. Moreover, we found no significant differences in the striatal levels of dopamine and its metabolites dihydroxyphenylacetic acid and homovanillic acid. Our results indicate that a combined haploinsufficiency for Tgfβ2 and Gdnf has no impact on the function and the survival of midbrain DA neurons under normal aging conditions.
Tgfβ2; Gdnf; Dopamine; Nigro-striatal system; Midbrain
Genetic variability in the α-synuclein gene and long-term exposure to the pesticide paraquat constitute possible risk factors for sporadic Parkinson’s disease. The goal of the present study was to further characterize the effects of paraquat in mice as a model of Parkinson’s disease and to determine whether it acted synergistically with α-synuclein over-expression to cause nigrostriatal cell death or dysfunction. Paraquat (10 mg/kg i.p.) was administered once a week for 3 weeks to mice over-expressing human α-synuclein under the Thy1 promoter and their wild-type littermates. The effect of paraquat on catecholaminergic neurons was reminiscent of that of Parkinson’s disease, with preferential loss of dopaminergic neurons in the ventral tier of the substantia nigra pars compacta and loss of tyrosine hydroxylase staining in the locus coeruleus. α-Synuclein over-expression did not increase paraquat-induced cell loss, and paraquat did not worsen the behavioral deficits observed in the transgenic mice. However, paraquat markedly increased proteinase-K-resistant α-synuclein aggregates in substantia nigra of the transgenic mice. The data further validate the use of paraquat to model Parkinson’s disease in mice and show that although paraquat and α-synuclein over-expression act synergistically to increase protein aggregation in vivo, this interaction does not result in short-term neuroprotection or increased vulnerability of nigrostriatal neurons.
pesticide; Parkinson’s disease; substantia nigra; striatum; locus coeruleus; mice
Parkinson’s disease (PD) results from the loss of dopamine neurons located in the substantia nigra pars compacta (SNpc) that project to the striatum. A therapeutic has yet to be identified that halts this neurodegenerative process, and as such, development of a brain penetrant small molecule neuroprotective agent would represent a significant advancement in the treatment of the disease. To fill this void we developed an aminopyrimidine JNK inhibitor (SR-3306) that reduced the loss of dopaminergic cell bodies in the SNpc and their terminals in the striatum produced by unilateral injection of 6-hydroxydopamine (6-OHDA) into the nigrostriatal pathway. Administration of SR-3306 [10 mg/kg/day (s.c.) for 14 days] increased the number of tyrosine hydroxylase immunoreactive (TH+) neurons in the SNpc by six-fold and reduced the loss of the TH+ terminals in the striatum relative to the corresponding side of 6-OHDA-lesioned rats that received only vehicle (p<0.05). In addition, SR-3306 [10 mg/kg/day (s.c.) for 14 days] decreased d-amphetamine-induced circling by 87% compared to 6-OHDA-lesioned animals given vehicle. Steady-state brain levels of SR-3306 at day 14 were 347 nM, which was approximately two-fold higher than the cell-based IC50 for this compound. Finally, immunohistochemical staining for phospho-c-jun (p-c-jun) revealed that SR-3306 [10 mg/kg/day (s.c.) for 14 days] produced a 2.3-fold reduction of the number of immunoreactive neurons in the SNpc relative to vehicle treated rats. Collectively, these data suggest that orally bioavailable JNK inhibitors may be useful neuroprotective agents for the treatment of Parkinson’s disease.
Parkinson’s disease (PD) results from the loss of dopamine neurons located in the substantia nigra pars compacta (SNpc) that project to the striatum. A therapeutic has yet to be identified that halts this neurodegenerative process, and as such, development of a brain penetrant small molecule neuroprotective agent would represent a significant advancement in the treatment of the disease. To fill this void, we developed an aminopyrimidine JNK inhibitor (SR-3306) that reduced the loss of dopaminergic cell bodies in the SNpc and their terminals in the striatum produced by unilateral injection of 6-hydroxydopamine (6-OHDA) into the nigrostriatal pathway. Administration of SR-3306 [10 mg/kg/day (s.c.) for 14 days] increased the number of tyrosine hydroxylase immunoreactive (TH+) neurons in the SNpc by 6-fold and reduced the loss of the TH+ terminals in the striatum relative to the corresponding side of 6-OHDA-lesioned rats that received only vehicle (p < 0.05). In addition, SR-3306 [10 mg/kg/day (s.c.) for 14 days] decreased d-amphetamine-induced circling by 87% compared to 6-OHDA-lesioned animals given vehicle. Steady-state brain levels of SR-3306 at day 14 were 347 nM, which was approximately 2-fold higher than the cell-based IC50 for this compound. Finally, immunohistochemical staining for phospho-c-jun (p-c-jun) revealed that SR-3306 [10 mg/kg/day (s.c.) for 14 days] produced a 2.3-fold reduction of the number of immunoreactive neurons in the SNpc relative to vehicle treated rats. Collectively, these data suggest that orally bioavailable JNK inhibitors may be useful neuroprotective agents for the treatment of Parkinson’s disease.
JNK; 6-OHDA; neuroprotection; Parkinson’s disease
Background: Melatonin has receptors in substantia nigra pars compacta (SNc) and regulates development of dopaminergic (DA) neurons. This study was undertaken to determine ability of melatonin to protect SNc dopaminergic neuron loss induced by estrogen deficiency in ovariectomized rats. Methods: Female rats were randomized into four groups of seven each: control, ethanol sham, ovariectomy (ovx) and ovx with melatonin (ovx + m). In ovx, ovaries were removed. Ovx + m group was intraperitoneally injected with melatonin for 10 days, while the ethanol sham group received only ethanol. All rats were perfused with 4% paraformaldehyde, midbrains removed, fixed and paraffin embedded, then processed for Nissl and tyrosine hydroxylase staining (IHC). Ten sections of SNc in Nissl and IHC staining were analyzed in each animal, Nissl stained and tyrosine hydroxylase (TH) immunoreactive cells were counted in five experimental groups randomly. Data was analyzed using SPSS by ANOVA and t-test. Differences were considered significant for P<0.05. Results: There was less cell number in ovx compared to control and ethanol sham groups significantly (P<0.001). The ovx + m group had more cells than the ovx group in the SNc significantly (P<0.001). Furthermore, there was significant decrease of TH positive cell number in the ovx group compared to control and ethanol sham groups (P<0.05). The number of TH immunoreactive cells was higher in ovx + m compared to the ovx group (P<0.05). Conclusion: These findings can be compared with human and used in clinical application for prevention of DA neuron death of SNc after ovariectomy.
Exogenous melatonin; Substantia nigra; Dopaminergic neurons (DA); Ovariectomized rat; Morphometric analysis
Reactive oxygen species (ROS), superoxide and hydrogen peroxide (H2O2), are necessary for appropriate responses to immune challenges. In the brain, excess superoxide production predicts neuronal cell loss, suggesting that Parkinson's disease (PD) with its wholesale death of dopaminergic neurons in substantia nigra pars compacta (nigra) may be a case in point. Although microglial NADPH oxidase-produced superoxide contributes to dopaminergic neuron death in an MPTP mouse model of PD, this is secondary to an initial die off of such neurons, suggesting that the initial MPTP-induced death of neurons may be via activation of NADPH oxidase in neurons themselves, thus providing an early therapeutic target.
NADPH oxidase subunits were visualized in adult mouse nigra neurons and in N27 rat dopaminergic cells by immunofluorescence. NADPH oxidase subunits in N27 cell cultures were detected by immunoblots and RT-PCR. Superoxide was measured by flow cytometric detection of H2O2-induced carboxy-H2-DCFDA fluorescence. Cells were treated with MPP+ (MPTP metabolite) following siRNA silencing of the Nox2-stabilizing subunit p22phox, or simultaneously with NADPH oxidase pharmacological inhibitors or with losartan to antagonize angiotensin II type 1 receptor-induced NADPH oxidase activation.
Nigral dopaminergic neurons in situ expressed three subunits necessary for NADPH oxidase activation, and these as well as several other NADPH oxidase subunits and their encoding mRNAs were detected in unstimulated N27 cells. Overnight MPP+ treatment of N27 cells induced Nox2 protein and superoxide generation, which was counteracted by NADPH oxidase inhibitors, by siRNA silencing of p22phox, or losartan. A two-wave ROS cascade was identified: 1) as a first wave, mitochondrial H2O2 production was first noted at three hours of MPP+ treatment; and 2) as a second wave, H2O2 levels were further increased by 24 hours. This second wave was eliminated by pharmacological inhibitors and a blocker of protein synthesis.
A two-wave cascade of ROS production is active in nigral dopaminergic neurons in response to neurotoxicity-induced superoxide. Our findings allow us to conclude that superoxide generated by NADPH oxidase present in nigral neurons contributes to the loss of such neurons in PD. Losartan suppression of nigral-cell superoxide production suggests that angiotensin receptor blockers have potential as PD preventatives.
Significance: Parkinson's disease (PD) is a neurodegenerative disorder characterized, in part, by the progressive and selective loss of dopaminergic neuron cell bodies within the substantia nigra pars compacta (SNpc) and the associated deficiency of the neurotransmitter dopamine (DA) in the striatum, which gives rise to the typical motor symptoms of PD. The mechanisms that contribute to the induction and progressive cell death of dopaminergic neurons in PD are multi-faceted and remain incompletely understood. Data from epidemiological studies in humans and molecular studies in genetic, as well as toxin-induced animal models of parkinsonism, indicate that mitochondrial dysfunction occurs early in the pathogenesis of both familial and idiopathic PD. In this review, we provide an overview of toxin models of mitochondrial dysfunction in experimental Parkinson's disease and discuss mitochondrial mechanisms of neurotoxicity. Recent Advances: A new toxin model using the mitochondrial toxin trichloroethylene was recently described and novel methods, such as intranasal exposure to toxins, have been explored. Additionally, recent research conducted in toxin models of parkinsonism provides an emerging emphasis on extranigral aspects of PD pathology. Critical Issues: Unfortunately, none of the existing animal models of experimental PD completely mimics the etiology, progression, and pathology of human PD. Future Directions: Continued efforts to optimize established animal models of parkinsonism, as well as the development and characterization of new animal models are essential, as there still remains a disconnect in terms of translating mechanistic observations in animal models of experimental PD into bona fide disease-modifying therapeutics for human PD patients. Antioxid. Redox Signal. 16, 920–934.
Parkinson’s disease is a neurodegenerative movement disorder that is caused, in part, by the loss of dopaminergic neurons within the substantia nigra pars compacta of the basal ganglia. The presence of intracellular protein aggregates, known as Lewy bodies and Lewy neurites, within the surviving nigral neurons is the defining neuropathological feature of the disease. Accordingly, the identification of specific genes mutated in families with Parkinson’s disease and of genetic susceptibility variants for idiopathic Parkinson’s disease has implicated abnormalities in proteostasis, or the handling and elimination of misfolded proteins, in the pathogenesis of this neurodegenerative disorder. Protein folding and the refolding of misfolded proteins are regulated by a network of interactive molecules, known as the chaperone system, which is composed of molecular chaperones and co-chaperones. The chaperone system is intimately associated with the ubiquitin-proteasome system and the autophagy-lysosomal pathway which are responsible for elimination of misfolded proteins and protein quality control. In addition to their role in proteostasis, some chaperone molecules are involved in the regulation of cell death pathways. Here we review the role of the molecular chaperones Hsp70 and Hsp90, and the co-chaperones Hsp40, BAG family members such as BAG5, CHIP and Hip in modulating neuronal death with a focus on dopaminergic neurodegeneration in Parkinson’s disease. We also review current progress in preclinical studies aimed at targetting the chaperone system to prevent neurodegeneration. Finally, we discuss potential future chaperone-based therapeutics for the symptomatic treatment and possible disease modification of Parkinson’s disease.
Bcl-2 associated athanogene (BAG) family; C-terminal Hsp70 interacting protein (CHIP); chaperones; co-chaperones; heat shock protein (Hsp); Hsp90 inhibitors; neurodegeneration; Parkinson’s disease
Reelin, an extracellular glycoprotein has an important role in the proper migration and positioning of neurons during brain development. Lack of reelin causes not only disorganized lamination of the cerebral and cerebellar cortex but also malpositioning of mesencephalic dopaminergic (mDA) neurons. However, the accurate role of reelin in the migration and positioning of mDA neurons is not fully elucidated. In this study, reelin-deficient reeler mice exhibited a significant loss of mDA neurons in the substantia nigra pars compacta (SNc) and a severe alteration of cell distribution in the retrorubal field (RRF). This abnormality was also found in Dab1-deficinet, yotari mice. Stereological analysis revealed that total number of mDA neurons was not changed compared to wild type, suggesting that the loss of mDA neurons in reeler may not be due to the neurogenesis of mDA neurons. We also found that formation of PSA-NCAM-positive tangential nerve fibers rather than radial glial fibers was greatly reduced in the early developmental stage (E14.5) of reeler. These findings provide direct evidence that the alteration in distribution pattern of mDA neurons in the reeler mesencephalon mainly results from the defect of the lateral migration using tangential fibers as a scaffold.
Reelin; dopaminergic neurons; radial glia; tangential fibers; neuronal migration
The pathology of Parkinson's disease (PD) is characterized by the degeneration of the nigrostriatal dopaminergic pathway, as well as the formation of intraneuronal inclusions known as Lewy bodies and Lewy neurites in the substantia nigra. Accumulations of nitrated α-synuclein are demonstrated in the signature inclusions of Parkinson's disease. However, whether the nitration of α-synuclein is relevant to the pathogenesis of PD is unknown.
In this study, effect of nitrated α-synuclein to dopaminergic (DA) neurons was determined by delivering nitrated recombinant TAT-α-synuclein intracellular. We provide evidence to show that the nitrated α-synuclein was toxic to cultured dopaminergic SHSY-5Y neurons and primary mesencephalic DA neurons to a much greater degree than unnitrated α-synuclein. Moreover, we show that administration of nitrated α-synuclein to the substantia nigra pars compacta of rats caused severe reductions in the number of DA neurons therein, and led to the down-regulation of D2R in the striatum in vivo. Furthermore, when administered to the substantia nigra of rats, nitrated α-synuclein caused PD-like motor dysfunctions, such as reduced locomotion and motor asymmetry, however unmodified α-synuclein had significantly less severe behavioral effects.
Our results provide evidence that α-synuclein, principally in its nitrated form, induce DA neuron death and may be a major factor in the etiology of PD.
OBJECTIVE—To test the
hypothesis that differential regional dopamine transporter (DAT) gene
expression may underlie the selective vulnerability of certain nigral
dopaminergic neurons in Parkinson's disease, DAT mRNA expression was
examined in neuronal subpopulations of human postmortem ventral
mesencephalon from patients with Parkinson's disease and controls.
in situ hybridisation histochemistry using a polymerase chain reaction
derived ribonucleotide probe for DAT was performed on sections of
ventral mesencephalon from the brains of five donors with no history of
neurological illness and from five patients with pathologically
established Parkinson's disease. The number of silver grains overlying
melanised neurons from the paranigral nucleus, dorsal and ventral tier,
and pars lateralis of the substantia nigra pars compacta were compared
with each other and to background labelling by using a one way
factorial analysis of variance (ANOVA) with a significance level of
brains, there was intense DAT mRNA expression in the ventral midbrain
with no significant difference in mRNA concentrations among the four regions studied. In the
Parkinson's disease brains, there was an overall decrease in the
intensity of DAT mRNA expression in the surviving dopaminergic neurons.
There were no significant differences in signal between regions in
either the control or parkinsonian brains.
together, these findings do not support the hypothesis that
differential regional DAT gene expression underlies the selective
vulnerability of certain nigral dopaminergic neurons in Parkinson's
disease, as the vulnerable neurons of the substantia nigra pars
compacta do not express more DAT mRNA than the resistant paranigral neurons.
Pleiotrophin is known to promote the survival and differentiation of dopaminergic neurons in vitro and is up-regulated in the substantia nigra of Parkinson's disease patients. To establish whether pleiotrophin has a trophic effect on nigrostriatal dopaminergic neurons in vivo, we injected a recombinant adenovirus expressing pleiotrophin in the substantia nigra of 6-hydroxydopamine lesioned rats.
The viral vector induced pleiotrophin over-expression by astrocytes in the substantia nigra pars compacta, without modifying endogenous neuronal expression. The percentage of tyrosine hydroxylase-immunoreactive cells as well as the area of their projections in the lesioned striatum was higher in pleiotrophin-treated animals than in controls.
These results indicate that pleiotrophin over-expression partially rescues tyrosine hydroxylase-immunoreactive cell bodies and terminals of dopaminergic neurons undergoing 6-hydroxydopamine-induced degeneration.
Dopamine is transported into synaptic vesicles by the vesicular monoamine transporter (VMAT2; SLC18A2). Disruption of dopamine storage has been hypothesized to damage the dopamine neurons that are lost in Parkinson's disease. By disrupting vesicular storage of dopamine and other monoamines, we have created a progressive mouse model of PD that exhibits catecholamine neuron loss in the substantia nigra pars compacta and locus coeruleus and motor and nonmotor symptoms. With a 95% reduction in VMAT2 expression, VMAT2-deficient animals have decreased motor function, progressive deficits in olfactory discrimination, shorter latency to behavioral signs of sleep, delayed gastric emptying, anxiety-like behaviors at younger ages, and a progressive depressive-like phenotype. Pathologically, the VMAT2-deficient mice display progressive neurodegeneration in the substantia nigra (SNpc), locus coeruleus (LC), and dorsal raphe (DR) coupled with α-synuclein accumulation. Taken together, these studies demonstrate that reduced vesicular storage of monoamines and the resulting disruption of the cytosolic environment may play a role in the pathogenesis of parkinsonian symptoms and neurodegeneration. The multisystem nature of the VMAT2-deficient mice may be useful in developing therapeutic strategies that go beyond the dopamine system.
Recent clinical evidence supports a link between 25-hydroxyvitamin D insufficiency (serum 25-hydroxyvitamin D [25(OH)D] levels <30 ng/mL) and Parkinson’s disease. To investigate the effect of 25(OH)D depletion on neuronal susceptibility to toxic insult, we induced a state of 25(OH)D deficiency in mice and then challenged them with the dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). We found there was no significant difference between control and 25(OH)D-deficient animals in striatal dopamine levels or dopamine transporter and tyrosine hydroxylase expression after lesioning with MPTP. Additionally, we found no difference in tyrosine hydroxylase expression in the substantia nigra pars compacta. Our data suggest that reducing 25(OH)D serum levels in mice has no effect on the vulnerability of nigral dopaminergic neurons in vivo in this model system of parkinsonism.
Characterizing dopaminergic neuronal development and function in novel genetic animal models might uncover strategies for researchers to develop disease-modifying treatments for neurologic disorders. Id2 is a transcription factor expressed in the developing central nervous system. Id2−/− mice have fewer dopaminergic neurons in the olfactory bulb and reduced olfactory discrimination, a pre-clinical marker of Parkinson’s disease. Here, we summarize behavioral, histological and in vitro molecular biological analyses to determine whether midbrain dopaminergic neurons are affected by Id2 loss. Id2−/− mice were hyperactive at 1 and 3 months of age, but by 6 months showed reduced activity. Id2−/− mice showed age-dependent histological alterations in dopaminergic neurons of the substantia nigra pars compacta (SNpC) associated with changes in locomotor activity. Reduced dopamine transporter (DAT) expression was observed at early ages in Id2−/− mice and DAT expression was dependent on Id2 expression in an in vitro dopaminergic differentiation model. Evidence of neurodegeneration, including activated caspase-3 and glial infiltration, were noted in the SNpC of older Id2−/− mice. These findings document a novel role for Id2 in the maintenance of midbrain dopamine neurons. The Id2−/− mouse should provide unique opportunities to study the progression of neurodegenerative disorders involving the dopamine system.
Parkinson’s disease (PD) is characterized by the progressive degeneration of substantia nigra pars compacta (SNpc) dopaminergic neurones and the formation of Lewy bodies (LB) in a proportion of the remaining neurones. α-synuclein is the main component of LB, but the pathological mechanisms that lead to neurodegeneration associated with LB formation remain unclear. Three pivotal elements have emerged in the development of PD: α-synuclein, mitochondria and protein degradation systems. We previously reported a unique model, created by conditional genetic depletion of 26S proteasomes in the SNpc of mice, which mechanistically links these three elements with the neuropathology of PD: progressive neurodegeneration and intraneuronal inclusion formation. Using this model, we tested the hypothesis that α-synuclein was essential for the formation of inclusions and neurodegeneration caused by 26S proteasomal depletion. We found that both of these processes were independent of α-synuclein. This provides an important insight into the relationship between the proteasome, α-synuclein, inclusion formation and neurodegeneration. We also show that the autophagy-lysosomal pathway is not activated in 26S proteasome-depleted neurones. This leads us to suggest that the paranuclear accumulation of mitochondria in inclusions in our model may reflect a role for the ubiquitin proteasome system in mitochondrial homeostasis and that neurodegeneration may be mediated through mitochondrial factors linked to inclusion biogenesis.
Parkinson disease (PD) is the most common movement disorder. It is characterized by bradykinesia, postural instability, resting tremor, and rigidity associated with the progressive loss of dopaminergic neurons in the substantia nigra pars compacta. Another pathological hallmark of PD is the presence of α-synuclein proteiniacous inclusions, known as Lewy bodies and Lewy neurites, in some of the remaining dopaminergic neurons. Mounting evidence indicates that both genetic and environmental factors contribute to the etiology of PD. For example, genetic mutations (duplications, triplications or missense mutations) in the α-synuclein gene can lead to PD, but even in these patients age-dependent physiological changes or environmental exposures appear to be involved in disease presentation. Several additional alterations in many other genes have been established to either cause or increase the risk of Parkinson disease. More specifically, autosomal dominant missense mutations in the gene for leucine-rich repeat kinase 2 (LRRK2/PARK8) are the most common known cause of PD. Recently it was shown that G2019S, the most common diseasing-causing mutant of LRRK2, has dramatic effects on the kinase activity of LRRK2: while activity of wild-type LRRK2 is inhibited by manganese, the G2019S mutation abrogates this inhibition. Based on the in vitro kinetic properties of LRRK2 in the presence of manganese, we proposed that LRRK2 may be a sensor of cytoplasmic manganese levels and that the G2019S mutant has lost this function. This finding, alongside a growing number of studies demonstrating an interaction between PD-associated proteins and manganese, suggest that dysregulation of neuronal manganese homeostasis over a lifetime can play an important role in the etiology of PD.
Parkinson disease; mutation; α-synuclein; LRRK2; manganese; toxicity
The long-term consequences of forebrain ischemia include delayed Parkinson's syndrome. This study revealed delayed neurodegeneration in the substantia nigra 8 weeks after 12.5 minutes of global ischemia in rat brain. Following neuronal loss of 30–40% in central and dorsolateral striatum at day 3, neuronal damage in the substantia nigra (SN) was assessed at 4–8 weeks using immunohistochemistry for glutamate decarboxylase 67 (GAD67), vesicular GABA transporter (VGAT), and calretinin (CR). At day 56, the optical density of GAD67-, but not VGAT-, immunoreactivity in substantia nigra pars reticulata (SNR)—significantly decreased. CR-neurons concentrated in substantia nigra pars compacta (SNC) were reduced by 27% from day 3 (n = 5) to day 56 (n = 7, ANOVA, p < .01). Movement coordination was impaired at day 56, as evaluated using beam-walking test (time-to-traverse 5.6 ± 1.2 sec versus 11.8 ± 5.4 sec; sham versus ischemia, p < .05, n = 5, and 7, resp.). Our results demonstrate delayed impairment of the GABAergic system components in SN and associated with movement deficits after global ischemia.
The fibroblast growth factor (FGF) family comprises 22 members with diverse functions in development and metabolism. Fgf20 was originally identified as a new Fgf preferentially expressed in the substantia nigra pars compacta (SNpc). Fgf20, which acts on proximal cells, significantly enhanced the survival of cultured dopaminergic neurons by activating the mitogen-activated protein kinase (MAPK) pathway through Fgf receptor 1c. In the rat model of Parkinson's disease, Fgf20 afforded significant protection against the loss of dopaminergic neurons. The significant correlation of Parkinson's disease with single-nucleotide polymorphisms in FGF20 indicates that the genetic variability of FGF20 can be a Parkinson's disease risk. Neural and embryonic stem (ES) cells have been considered as cell resources for restorative transplantation strategies in Parkinson's disease. Fgf20 promoted the differentiation of these stem cells into dopaminergic neurons, which attenuated neurological symptoms in animal models of Parkinson's disease. These findings indicate the importance of FGF20 for the differentiation and survival of dopaminergic neurons and the etiology and therapy of Parkinson's disease.
dopaminergic neurons; Fgf; Fgf20; Parkinson's disease; stem cells; SNP
The male sex is determined by the sex determining region on the Y chromosome (SRY) transcription factor. The unexpected action of SRY in the control of voluntary movement in male rodents suggests a role in regulation of dopamine transmission and dopamine-related disorders with sex bias such as Parkinson’s disease. We investigated SRY expression in the human brain and function in vitro. SRY immunoreactivity was detected in the human male, but not female, substantia nigra pars compacta (SNc) within a sub-population of tyrosine hydroxylase (TH) positive neurons. SRY protein also co-localised with TH positive neurons in the ventral tegmental area and GAD-positive neurons in the substantia nigra pars reticulate (SNr). Retinoic acid-induced differentiation of precursor NT2 cells into dopaminergic cells (NT2N) increased expression of TH, NURR1, D2R and SRY. In the human neuroblastoma cell line, M17, SRY knockdown resulted in a reduction in TH, DDC, DBH and MAO-A expression; enzymes which control dopamine synthesis and metabolism. Conversely, SRY overexpression increased TH, DDC, DBH, D2R and MAO-A levels, which was accompanied by increased extracellular dopamine levels. A luciferase assay demonstrated that SRY activated a 4.6 kb 5′ upstream regulatory region of the human TH promoter/nigral enhancer. Combined, these results suggest that SRY may play a role as a positive regulator of catecholamine synthesis and metabolism in the human male midbrain. Given the limitations of human tissue analysis, further studies are required to provide a definitive answer on SRY expression in human brain regions.
sex determination; basal ganglia; sexual dimorphism; catecholamine; dopamine; addiction
Recent studies have demonstrated the molecular basis of the immunomodulatory and anti-inflammatory activities of 1,25-dihydroxyvitamin D3(1,25-(OH)2D3). This hormone improves behavioral deficits and normalizes the nigral dopamine levels in animal models of Parkinson's disease (PD).
We studied whether the administration of 1,25-(OH)2D3 would protect against 6-hydroxydopa (6-OHDA)- and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neuronal injury, and its potential regulatory effect on microglia activation.
We found that 1,25-(OH)2D3 pretreatment significantly decreased 6-OHDA- and MPTP-induced dopaminergic neuronal loss in the substantia nigra pars compacta by preventing the activation of microglia. This observed neuroprotective effect in MPTP-treated mice that were given 1,25-(OH)2D3 may be attributable to inhibition of proinflammatory cytokine expression.
These results suggest that 1,25-(OH)2D3 is a potentially valuable neuroprotective agent; it may therefore be considered for the treatment of pathologic conditions of the central nervous system, such as PD, where inflammation-induced neurodegeneration occurs.
Vitamin D; Parkinson's disease; 6-hydroxydopa (6-OHDA); 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP); Cytokine; Inflammation; Rat; Mouse
Parkinson’s disease (PD) is a progressive neurodegenerative disease caused by the interaction of genetic and environmental factors. However, the etiology of PD remains largely unknown. Macroautophagy is known to play an essential role in the degradation of abnormal proteins and organelles. Furthermore, the loss of autophagy-related (Atg) genes results in neurodegeneration and abnormal protein accumulation. Since these are also pathologic features of Parkinson disease, the conditional impairment of autophagy may lead to improved animal models for the study of PD. Using transgenic mice expressing Cre recombinase under the control of either the dopamine transporter or the engrailed-1 promoters, we generated mice with the conditional deletion of Atg7 in the dopamine neurons of the substantia nigra pars compacta, other regions of the midbrain, and also the hindbrain. This conditional impairment of autophagy results in the age-related loss of dopaminergic neurons and corresponding loss of striatal dopamine, the accumulation of low molecular weight α-synuclein, and the presence of ubiquitinated protein aggregates, recapitulating many of the pathologic features of PD. These conditional knockout animals provide insight into the process of autophagy in Parkinson disease pathology.
A large body of evidence suggests that mitochondrial dysfunction and oxidative damage play a role in the pathogenesis of Parkinson's disease (PD). A number of antioxidants have been effective in animal models of PD. We have developed a family of mitochondria-targeted peptides that can protect against mitochondrial swelling and apoptosis (SS peptides). In this study, we examined the ability of two peptides, SS-31 and SS-20, to protect against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxicity in mice. SS-31 produced dose-dependent complete protection against loss of dopamine and its metabolites in striatum, as well as loss of tyrosine hydroxylase immunoreactive neurons in substantia nigra pars compacta. SS-20, which does not possess intrinsic ability in scavenging reactive oxygen species, also demonstrated significant neuroprotective effects on dopaminergic neurons of MPTP-treated mice. Both SS-31 and SS-20 were very potent (nM) in preventing MPP+ (1-methyl-4-phenylpyridinium)-induced cell death in cultured dopamine cells (SN4741). Studies with isolated mitochondria showed that both SS-31 and SS-20 prevented MPP+-induced inhibition of oxygen consumption and ATP production, and mitochondrial swelling. These findings provide strong evidence that these neuroprotective peptides, which target both mitochondrial dysfunction and oxidative damage, are a promising approach for the treatment of PD. Antioxid. Redox Signal. 11, 2095–2104.
Parkinson's disease is characterized by a progressive loss of dopaminergic neurons in the substantia nigra zona compacta, and in other sub-cortical nuclei associated with a widespread occurrence of Lewy bodies. The cause of cell death in Parkinson's disease is still poorly understood, but a defect in mitochondrial oxidative phosphorylation and enhanced oxidative and nitrative stresses have been proposed. We have studied controlwt (C57B1/6), metallothionein transgenic (MTtrans), metallothionein double gene knock (MTdko), α-synuclein knock out (α-synko), α-synuclein–metallothionein triple knock out (α-syn–MTtko), weaver mutant (wv/wv) mice, and Ames dwarf mice to examine the role of peroxynitrite in the etiopathogenesis of Parkinson's disease and aging. Although MTdko mice were genetically susceptible to 1, methyl, 4-phenyl, 1,2,3,6-tetrahydropyridine (MPTP) Parkinsonism, they did not exhibit any overt clinical symptoms of neurodegeneration and gross neuropathological changes as observed in wv/wv mice. Progressive neurodegenerative changes were associated with typical Parkinsonism in wv/wv mice. Neurodegenerative changes in wv/wv mice were observed primarily in the striatum, hippocampus and cerebellum. Various hallmarks of apoptosis including caspase-3, TNFα, NFκB, metallothioneins (MT-1, 2) and complex-1 nitration were increased; whereas glutathione, complex-1, ATP, and Ser(40)-phosphorylation of tyrosine hydroxylase, and striatal 18F-DOPA uptake were reduced in wv/wv mice as compared to other experimental genotypes. Striatal neurons of wv/wv mice exhibited age-dependent increase in dense cored intra-neuronal inclusions, cellular aggregation, proto-oncogenes (c-fos, c-jun, caspase-3, and GAPDH) induction, inter-nucleosomal DNA fragmentation, and neuro-apoptosis. MTtrans and α-Synko mice were genetically resistant to MPTP-Parkinsonism and Ames dwarf mice possessed significantly higher concentrations of striatal coenzyme Q10 and metallothioneins (MT 1, 2) and lived almost 2.5 times longer as compared to controlwt mice. A potent peroxynitrite ion generator, 3-morpholinosydnonimine (SIN-1)-induced apoptosis was significantly attenuated in MTtrans fetal stem cells. These data are interpreted to suggest that peroxynitrite ions are involved in the etiopathogenesis of Parkinson's disease, and metallothionein-mediated coenzyme Q10 synthesis may provide neuroprotection.
Metallothionein double gene knockout mice; Metallothionein transgenic mice; α -synuclein knockout mice; Homozygous weaver mutant mice (WMhomo); Ames dwarf mice; Fetal stem cell transplantation; 18F-DOPA; MicroPET imaging; Parkinson's disease