KDS2010, a Newly Developed Reversible MAO-B Inhibitor, as an Effective Therapeutic Candidate for Parkinson's Disease

Monoamine oxidase-B (MAO-B) is a well-established therapeutic target for Parkinson's disease (PD); however, previous clinical studies on currently available irreversible MAO-B inhibitors have yielded disappointing neuroprotective effects. Here, we tested the therapeutic potential of KDS2010, a recently synthesized potent, selective, and reversible MAO-B inhibitor in multiple animal models of PD. We designed and synthesized a series of α-aminoamide derivatives and found that derivative KDS2010 exhibited the highest potency, specificity, reversibility, and bioavailability (> 100%). In addition, KDS2010 demonstrated significant neuroprotective and anti-neuroinflammatory efficacy against nigrostriatal pathway destruction in the mouse MPTP model of parkinsonism. Treatment with KDS2010 also alleviated parkinsonian motor dysfunction in 6-hydroxydopamine-induced and A53T mutant α-synuclein overexpression rat models of PD. Moreover, KDS2010 showed virtually no toxicity or side effects in non-human primates. KDS2010 could be a next-generation therapeutic candidate for PD.

Docosahexaenoic acid protects motor function and increases dopamine synthesis in a rat model of Parkinson's disease via mechanisms associated with increased protein kinase activity in the striatum

Parkinson's disease (PD) is a devastating neurodegenerative disease that leads to motor deficits and selective destruction of nigrostriatal dopaminergic neurons. PD is typically treated by dopamine replacement agents; however, dopamine replacement loses effectiveness in the later stages of the disease. Here, we describe the neuroprotective effects of the omega-3 fatty acid docosahexaenoic acid (DHA) in the medial forebrain bundle 6-hydroxydopamine (6-OHDA) model of advanced-stage PD in rats. We show that daily administration of DHA protects against core symptoms of PD, including deficits in postural stability, gait integrity, and dopamine neurochemistry in motor areas of the striatum. Our results also demonstrate that DHA increases striatal dopamine synthesis via phosphorylation of the rate-limiting catecholamine synthesizing enzyme tyrosine hydroxylase, in a manner dependent on the second messenger-linked protein kinases PKA and PKC. We also show that DHA specifically reverses dopamine loss in the nigrostriatal pathway, with no effect in the mesolimbic or mesocortical pathways. This suggests that DHA is unlikely to produce pharmacotherapeutic or adverse effects that depend on dopamine pathways other than the nigrostriatal pathway. To our knowledge, previous reports have not examined the effects of DHA in such an advanced-stage model, documented that the dopamine synthesizing effects of DHA in vivo are mediated through the activation of protein kinases and regulation of TH activity, or demonstrated specificity to the nigrostriatal pathway. These novel findings corroborate the beneficial effects of omega-3 fatty acids seen in PD patients and suggest that DHA provides a novel means of protecting patients for dopamine neurodegeneration.

Association of Low Lysosomal Enzymes Activity With Brain Arterial Dilatation

Background and Purpose- Absent or diminished α-galactosidase A (GLA) and acid α-glucosidase (GAA) enzyme activity are core features of Fabry and Pompe disease, respectively. Patients with Fabry or Pompe disease may have dilated intracranial arteries but whether lower GLA or GAA enzyme activity relates to brain arterial dilatation in other populations is unknown. Methods- Participants included Parkinson disease patients and nonblood-related controls, whose GLA and GAA enzymatic activities were measured in dried blood spots. Independent readers measured the axial arterial diameter of the ascending portion of the cavernous internal carotid arteries and the most proximal segment of the basilar artery in T2 black voids. Linear regression models were built to investigate the relationship between brain arterial diameters and lysosomal enzymatic activities. Results- The cohort included 107 participants (mean age, 66.5±10.3; 67% men). In an adjusted linear regression model, lower GLA activity was associated with larger brain arterial diameters (B=0.50±0.23, P=0.03). The strength of association was the greatest for the basilar artery diameter (B=0.80±0.33, P=0.02). Similarly, lower GAA activity was associated with an increased basilar arterial diameter (B=0.73±0.35, P=0.04). Conclusions- Lower GLA and GAA enzymatic activities were associated with larger brain arterial diameters, particularly the basilar artery diameter. Lower lysosomal enzymatic function in patients without Fabry or Pompe disease may play a role in brain arterial dilatation.

Suppressing nNOS Enzyme by Small-Interfering RNAs Protects SH-SY5Y Cells and Nigral Dopaminergic Neurons from 6-OHDA Injury

Nitric oxide (NO) has chemical properties that make it uniquely suitable as an intracellular and intercellular messenger. NO is produced by the activity of the enzyme nitric oxide synthases (NOS). There is substantial and mounting evidence that slight abnormalities of NO may underlie a wide range of neurodegenerative disorders. NO participates of the oxidative stress and inflammatory processes that contribute to the progressive dopaminergic loss in Parkinson's disease (PD). The present study aimed to evaluate in vitro and in vivo the effects of neuronal NOS-targeted siRNAs on the injury caused in dopaminergic neurons by the toxin 6-hidroxydopamine (6-OHDA). First, we confirmed (immunohistochemistry and Western blotting) that SH-SY5Y cell lineage expresses the dopaminergic marker tyrosine hydroxylase (TH) and the protein under analysis, neuronal NOS (nNOS). We designed four siRNAs by using the BIOPREDsi algorithm choosing the one providing the highest knockdown of nNOS mRNA in SH-SY5Y cells, as determined by qPCR. siRNA 4400 carried by liposomes was internalized into cells, caused a concentration-dependent knockdown on nNOS, and reduced the toxicity induced by 6-OHDA (p < 0.05). Regarding in vivo action in the dopamine-depleted animals, intra-striatal injection of siRNA 4400 at 4 days prior 6-OHDA produced a decrease in the rotational behavior induced by apomorphine. Finally, siRNA 4400 mitigated the loss of TH(+) cells in substantia nigra dorsal and ventral part. In conclusion, the suppression of nNOS enzyme by targeted siRNAs modified the progressive death of dopaminergic cells induced by 6-OHDA and merits further pre-clinical investigations as a neuroprotective approach for PD.

Ambroxol modulates 6-Hydroxydopamine-induced temporal reduction in Glucocerebrosidase (GCase) enzymatic activity and Parkinson's disease symptoms

Reduced glucocerebrosidase (GCase) enzymatic activity is found in sporadic cases of Parkinson's disease making GCase a serious risk factor for PD. GCase gene mutations constitute a major risk factor in early-onset PD but only account for 5-10% cases. Having enough evidence for construct and face validity, 6-OHDA-induced hemiparkinson's model may be useful to assess the GCase-targeting drugs in order to have new leads for treatment of PD. Ambroxol (AMB) is reported to increase GCase activity in different brain-regions. Therefore, we investigated anti-PD like effects of AMB as well as GCase activity in striatal and nigral tissues of rats in hemiparkinson's model. AMB was given a dose of 400 mg/kg per oral twice daily and SEL used as positive control was given in the dose of 10 mg/kg per oral daily from D-4 to D-27 after 6-OHDA administration. 6-OHDA reduced GCase activity in striatal and in a progressive manner in nigral tissues. AMB and SEL attenuated 6-OHDA-induced motor impairments, dopamine (DA) depletion and GCase deficiency. AMB and SEL also ameliorated 6-OHDA-induced mitochondrial dysfunction in terms of MTT reduction, α-synuclein pathology, loss of nigral cells, and intrinsic pathway of apoptosis by modulating cytochrome-C, caspase-9, and caspase-3 expressions. The results suggest that AMB attenuated 6-OHDA-induced GCase deficiency and PD symptoms. Therefore, the regenerative effects of AMB in dopamine toxicity may be due to its effects on GCase activity and mitochondrial function. Results indicate that SEL also has regenerative effect in the 6-OHDA model. Thus, GCase enzymatic activity is likely to be involved in the development of PD symptoms, and 6-OHDA-induced hemiparkinson's model may be used to evaluate compounds targeting GCase activity for management of PD symptoms.

NMDA receptor blockade ameliorates abnormalities of spike firing of subthalamic nucleus neurons in a parkinsonian nonhuman primate

N-methyl-D-aspartate receptors (NMDARs) are ion channels comprising tetrameric assemblies of GluN1 and GluN2 receptor subunits that mediate excitatory neurotransmission in the central nervous system. Of the four different GluN2 subunits, the GluN2D subunit-containing NMDARs have been suggested as a target for antiparkinsonian therapy because of their expression pattern in some of the basal ganglia nuclei that show abnormal firing patterns in the parkinsonian state, specifically the subthalamic nucleus (STN). In this study, we demonstrate that blockade of NMDARs altered spike firing in the STN in a male nonhuman primate that had been rendered parkinsonian by treatment with the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. In accompanying experiments in male rodents, we found that GluN2D-NMDAR expression in the STN was reduced in acutely or chronically dopamine-depleted animals. Taken together, our data suggest that blockade of NMDARs in the STN may be a viable antiparkinsonian strategy, but that the ultimate success of this approach may be complicated by parkinsonism-associated changes in NMDAR expression in the STN.

Impaired CBS-H2S signaling axis contributes to MPTP-induced neurodegeneration in a mouse model of Parkinson's disease

Hydrogen sulfide (H₂S), a novel neuromodulator, is linked to the pathogenesis of several neurodegenerative disorders. Exogenous application of H₂S exerts neuroprotection via anti-inflammation and anti-oxidative stress in animal and cellular models of Parkinson's disease (PD). However, the role of endogenous H₂S and the contribution of its various synthases in PD remain unclear. In the present study, we found a decline of plasma and striatal sulfide level in 1-methy-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induced PD mouse model. Interestingly, among the three H₂S generating enzymes, only cystathionine β-synthase (CBS) expression was largely reduced in the striatum of MPTP-treated mice. The in vitro study confirmed a significant decrease of CBS expression in 1-methyl-4-phenylpyridinium (MPP⁺)-stimulated astrocytes and microglia, but not in neurons or SH-SY5Y dopaminergic cells. Striatal CBS overexpression, elicited by stereotaxic delivery with Cbs gene using recombinant adeno-associated-virus (rAAV-Cbs), successfully enhanced the sulfide level in the striatum and partially rescued the MPTP-induced dopaminergic neurotoxicity in the midbrain. Specifically, striatal CBS overexpression alleviated the motor deficits and dopaminergic neuron losses in the nigro-striatal pathway, with a concomitant inhibition of glial activation in MPTP-treated mice. Furthermore, compared to rAAV-Vector, rAAV-Cbs injection reduced the aberrant accumulation of nitric oxide and 3-nitrotyrosine (an indicator of protein nitration) in the striatum of MPTP-treated mice. Notably, it also attenuated the increase of nitrated α-synuclein level in MPTP mice. The in vitro study demonstrated that lentivirus-mediated CBS overexpression elevated the sulfide generation in glial cells. Moreover, glial CBS overexpression offered protection to midbrain dopaminergic neurons through repressing nitric oxide overproduction in both glial and neuronal cells induced by MPP⁺. Taken together, our data suggest that impaired CBS-H₂S axis may contribute to the pathogenesis of PD, and that modulation of this axis may become a novel therapeutic approach for PD.

The evaluation of the changes in enzymatic antioxidant reserves and lipid peroxidation in chosen parts of the brain in an animal model of Parkinson disease

BACKGROUND

Parkinson's disease is a progressive neurodegenerative disorder, characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta. The causes of Parkinson's disease are not fully understood; however, increasing evidence implicates oxidative stress.

OBJECTIVES

The study was aimed at assessing the nature of the changes in the oxidation-antioxidant balance in the cerebral cortex, striatum, hippocampus, thalamus, and cerebellum in a rat model of Parkinson's disease (PD).

MATERIAL AND METHODS

Sixteen male Wistar rats were divided into 2 groups: Icontrol, IIParkinson's disease. The 8-weeks-old animals were decapitated, their brains removed and the following structures dissected and then frozen for further biochemical assays: cerebral cortex, striatum, hippocampus, thalamus and cerebellum. The activities of: the catalase (CAT), glutathione reductase (GR), glutathione peroxidase (GPx), glutathione S-transferase (GST), superoxide dismutase (SOD) and the isoenzymes: Cu/ZnSOD and MnSOD; together with the malondialdehyde (MDA) and the total oxidative status (TOS) concentrations were measured in each structure.

RESULTS

A significantly increased activities of SOD, Cu/ZnSOD, GST and reduced GR activity and an increase of MDA concentration were observed in the striatum of PD rats, comparing to the control group, combined with a significantly reduced activities of GR,SOD, Cu/ZnSOD and an increased GPX activity and MDA concentration in the hippocampus, a significantly lower GR, SOD, MnSOD, Cu/ZnSOD, and GST activities in the cerebral cortex. A significantly lower GR activity, higher CAT activity and MDA concentration in the thalamus and a significantly increased GR activity in the cerebellum were observed in PD rats compared to the corresponding control group.

CONCLUSIONS

Oxidative stress in PD involves many brain structures and various antioxidant enzymes and oxidative status parameters become dysfunctional, depending on the area of the brain, which might reflect the complexity of the clinical symptoms of PD.

Lysosomal Storage of Subunit c of Mitochondrial ATP Synthase in Brain-Specific Atp13a2-Deficient Mice

Kufor-Rakeb syndrome (KRS) is an autosomal recessive form of early-onset parkinsonism linked to the PARK9 locus. The causative gene for KRS is Atp13a2, which encodes a lysosomal type 5 P-type ATPase. We recently showed that KRS/PARK9-linked mutations lead to several lysosomal alterations, including reduced proteolytic processing of cathepsin D in vitro. However, it remains unknown how deficiency of Atp13a2 is connected to lysosomal impairments. To address this issue, we analyzed brain tissues of Atp13a2 conditional-knockout mice, which exhibited characteristic features of neuronal ceroid lipofuscinosis, including accumulation of lipofuscin positive for subunit c of mitochondrial ATP synthase, suggesting that a common pathogenic mechanism underlies both neuronal ceroid lipofuscinosis and Parkinson disease.

Targeting the cannabinoid CB2 receptor to attenuate the progression of motor deficits in LRRK2-transgenic mice

Most of cases of Parkinson's disease (PD) have a sporadic origin, with their causes mostly unknown, although overexposure to some environmental factors has been found to occur in some cases. Other forms of parkinsonism are the consequence of dominant or recessive mutations in specific genes, e.g. α-synuclein, parkin and, more recently, leucine-rich repeat kinase 2 (LRRK2), whose G2019S mutation represents the most prevalent form of late-onset, autosomal dominant familial PD. A transgenic mouse model expressing the G2019S mutation of LRRK2 is already available and apparently may represent a valuable experimental model for investigating PD pathogenesis and novel treatments. We designed a long-term study with these animals aimed at: (i) elucidating the changes experienced by the endocannabinoid signaling system in the basal ganglia during the progression of the disease in these mice, paying emphasis in the CB2 receptor, which has emerged as a promising target in PD, and (ii) evaluating the potential of compounds selectively activating this CB2 receptor, as disease-modifying agents in these mice. Our results unequivocally demonstrate that LRRK2 transgenic mice develop motor impairment consisting of small anomalies in rotarod performance (presumably reflecting a deficit in motor coordination and dystonia) and a strong deficiency in the hanging-wire test (reflecting muscle weakness), rather than hypokinesia which was difficult to be demonstrated in the actimeter. These behavioral responses occurred in absence of any evidence of reactive gliosis and neuronal losses, as well as synaptic deterioration in the basal ganglia, except an apparent impairment in autophagy reflected by elevated LAMP-1 immunolabelling in the striatum and substantia nigra. Furthermore, there were no changes in the status of the CB2 receptor, as well as in other elements of the endocannabinoid signaling, in the basal ganglia, but, paradoxically, the selective activation of this receptor partially reversed the deficits in the hanging-wire test of LRRK2 transgenic mice. This was accompanied by normalization in LAMP-1 immunolabelling in the basal ganglia, although it is possible that other CNS structures, remaining to be identified, are involved in the behavioral improvement. In summary, our data support the interest of the CB2 receptor as a potential pharmacological target in LRRK2 transgenic mice, although the neuronal substrates underlying these benefits might be not completely related to the basal ganglia and to the presumed parkinsonian features of these mice.

Protective effects of 2,3,5,4'-tetrahydroxystilbene-2-O-β-D-glucoside in the MPTP-induced mouse model of Parkinson's disease: Involvement of reactive oxygen species-mediated JNK, P38 and mitochondrial pathways

Parkinson's disease (PD) is characterized by the selective death of dopaminergic neurons in the substantia nigra pars compacta. Oxidative stress-induced neuron loss is thought to play a crucial role in the pathogenesis of PD. Previous work from our group suggests that 2,3,5,4'-tetrahydroxystilbene-2-O-β-D-glucoside (TSG), an active component extracted from a traditional Chinese herb, Polygonum multiflorum thunb, can attenuate 1-methyl-4-phenyl pyridium-induced apoptosis in the neuronal cell line PC12, by inhibiting reactive oxygen species generation and modulating c-Jun N-terminal kinases (JNK) activation. Here, we investigated the protective effects of TSG against 1-methyl-4-phenyl-1,2,3,6-tetrahydropypridine (MPTP)-induced loss of tyrosine hydroxylase positive cells in mice and the underlying mechanisms. The results showed that MPTP-induced loss of tyrosine hydroxylase positive cells and reactive oxygen species generation were prevented by TSG in a dose-dependent manner. The reactive oxygen species scavenger N-acetylcysteine could also mitigate reactive oxygen species generation. Moreover, JNK and P38 were activated by MPTP, but extracellular signal-regulated protein kinases phosphorylation did not change after MPTP treatment. TSG at different doses blocked the activation of JNK and P38. The protective effect of TSG was also associated with downregulation of the bax/bcl-2 ratio, reversed the release of cytochrome c and smac, and inhibited the activation of caspase-3, -6, and -9 induced by MPTP. In conclusion, our studies demonstrated that the protective effects of TSG in the MPTP-induced mouse model of PD are involved, at least in part, in controlling reactive oxygen species-mediated JNK, P38, and mitochondrial pathways.

Isoflavone Attenuates the Caspase-1 and Caspase-3 Level in Cell Model of Parkinsonism

The study has investigated the effect of isoflavone attenuates the caspase-1 and caspase-3 level in cell model of Parkinsonism. The subjects were PC12 cells. They were randomly divided into six groups: control, MPP(+) (250 μmol/L), isoflavone (10 μM), isoflavone (10 μM) + MPP(+) (250 μmol/L), Z-YVAD-CHO (10 nM) + MPP(+) group, and Z-DEVD-CHO (10 nM) + MPP(+) group. Cell viability was measured by MTT methods; the content of tyrosine hydroxylase was measured by immunocytochemistry method of avidinbiotin peroxidase complex; apoptosis ratio was measured by flow cytometry. The results showed that cell viability in the MPP(+) group was lower than in all other five groups. There was no difference in cell viability between isoflavone + MPP(+) and control group. Optical density of TH positive cells in isoflavone group was higher than in control, isoflavone + MPP(+), and MPP(+) only groups. The apoptosis ratio in the isoflavone + MPP(+) group and control group and the Z-YVAD-CHO + MPP(+) and Z-DEVD-CHO + MPP(+) group was similar, which was lower than in the MPP(+) group. The lowest apoptosis ratio was found in the isoflavone only group.

Phosphodiesterase 7 inhibition induces dopaminergic neurogenesis in hemiparkinsonian rats

Parkinson's disease is characterized by a loss of dopaminergic neurons in a specific brain region, the ventral midbrain. Parkinson's disease is diagnosed when approximately 50% of the dopaminergic neurons of the substantia nigra pars compacta (SNpc) have degenerated and the others are already affected by the disease. Thus, it is conceivable that all therapeutic strategies, aimed at neuroprotection, start too late. Therefore, an urgent medical need exists to discover new pharmacological targets and novel drugs with disease-modifying properties. In this regard, modulation of endogenous adult neurogenesis toward a dopaminergic phenotype might provide a new strategy to target Parkinson's disease by partially ameliorating the dopaminergic cell loss that occurs in this disorder. We have previously shown that a phosphodiesterase 7 (PDE7) inhibitor, S14, exerts potent neuroprotective and anti-inflammatory effects in different rodent models of Parkinson's disease, indicating that this compound could represent a novel therapeutic agent to stop the dopaminergic cell loss that occurs during the progression of the disease. In this report we show that, in addition to its neuroprotective effect, the PDE7 inhibitor S14 is also able to induce endogenous neuroregenerative processes toward a dopaminergic phenotype. We describe a population of actively dividing cells that give rise to new neurons in the SNpc of hemiparkinsonian rats after treatment with S14. In conclusion, our data identify S14 as a novel regulator of dopaminergic neuron generation.

SIGNIFICANCE

Parkinson's disease is a neurodegenerative disorder characterized by the loss of dopaminergic neurons in the ventral midbrain. Currently, no cure and no effective disease-modifying therapy are available for Parkinson's disease; therefore, an urgent medical need exists to discover new pharmacological targets and novel drugs for the treatment of this disorder. The present study reports that an inhibitor of the enzyme phosphodiesterase 7 (S14) induces proliferation in vitro and in vivo of neural stem cells, promoting its differentiation toward a dopaminergic phenotype and therefore enhancing dopaminergic neuron generation. Because this drug is also able to confer neuroprotection of these cells in animal models of Parkinson's disease, S14 holds great promise as a therapeutic new strategy for this disorder.

The neuroprotective effect of lovastatin on MPP(+)-induced neurotoxicity is not mediated by PON2

Parkinson's disease (PD) is a neurodegenerative disorder characterized by loss of the pigmented dopaminergic neurons in the substantia nigra pars compacta with subsequent striatal dopamine (DA) deficiency and increased lipid peroxidation. The etiology of the disease is still unclear and it is thought that PD may be caused by a combination of genetic and environmental factors. In the search of new pharmacological options, statins have been recognized for their potential application to treat PD, due to their antioxidant effect. The aim of this work is to contribute in the characterization of the neuroprotective effect of lovastatin in a model of PD induced by 1-methyl-4-phenylpyridinium (MPP(+)). Male Wistar rats (200-250 g) were randomly allocated into 4 groups and administered for 7 days with different pharmacological treatments. Lovastatin administration (5 mg/kg) diminished 40% of the apomorphine-induced circling behavior, prevented the striatal DA depletion and lipid peroxides formation by MPP(+) intrastriatal injection, as compared to the group of animals treated only with MPP(+). Lovastatin produced no change in paraoxonase-2 (PON2) activity. It is evident that lovastatin conferred neuroprotection against MPP(+)-induced protection but this effect was not associated with the induction of PON2 in the rat striatum.

Neuroprotective effect of fasudil on inflammation through PI3K/Akt and Wnt/β-catenin dependent pathways in a mice model of Parkinson's disease

OBJECTIVE

Fasudil, a Rho kinase inhibitor, has neuroprotection in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-based Parkinson's disease (PD). This study aims to investigate the mechanism underlying the neuroprotection of fasudil in the PD mice model.

METHODS

Female MPTP-intoxication C57BL/6 mice were treated with normal saline or fasudil on day 15 after first administration of MPTP. Pole test was used for the behavioral analysis of mice. Expression of interleukin-1β (IL-1β) and tumor necrosis factor alpha (TNF-α) in brain tissue were detected by ELISA. Expression of tyrosine hydroxylase (TH), p-MYPT1, p-nuclear transcription factor NF-κB, toll-like receptor 2 (TLR2), arginase1, inducible nitric oxide synthase (iNOS), bromodeoxyuridine (BrdU), glial cell line-derived neurotrophic factor (GDNF), p-GSK-3b, p110-PI3K, p-Akt, WNT1, Fzd1 and β-catenin were determined by western blot and immunofluorescence analysis.

RESULTS

Fasudil enhanced the number of TH neurons which was decreased by MPTP treatment. Behavioral test showed that the motor performance of mice was improved after fasudil treatment. The expression of IL-1β, TNF-α, TLR2 and p-NF-κB and iNOS were lower after fasudil treatment (P<0.05) while the expression of arginase1 was increased (P<0.05). Further, we could observe the increase of GDNF expression in the microglial cells. The expression of p110-PI3K, p-Akt, WNT1, Fzd1 and β-catenin were increased after fasudil administration (P<0.05) in MPTP-based mice model.

CONCLUSIONS

Maybe fasudil protect dopamine neurons from loss in the MPTP mice model of PD through inflammatory inhibition via activation of PI3K/p-Akt and WNT1/Fzd1/β-catenin cell signaling pathways.

Functional reorganization of motor and limbic circuits after exercise training in a rat model of bilateral parkinsonism

Exercise training is widely used for neurorehabilitation of Parkinson's disease (PD). However, little is known about the functional reorganization of the injured brain after long-term aerobic exercise. We examined the effects of 4 weeks of forced running wheel exercise in a rat model of dopaminergic deafferentation (bilateral, dorsal striatal 6-hydroxydopamine lesions). One week after training, cerebral perfusion was mapped during treadmill walking or at rest using [(14)C]-iodoantipyrine autoradiography. Regional cerebral blood flow-related tissue radioactivity (rCBF) was analyzed in three-dimensionally reconstructed brains by statistical parametric mapping. In non-exercised rats, lesions resulted in persistent motor deficits. Compared to sham-lesioned rats, lesioned rats showed altered functional brain activation during walking, including: 1. hypoactivation of the striatum and motor cortex; 2. hyperactivation of non-lesioned areas in the basal ganglia-thalamocortical circuit; 3. functional recruitment of the red nucleus, superior colliculus and somatosensory cortex; 4. hyperactivation of the ventrolateral thalamus, cerebellar vermis and deep nuclei, suggesting recruitment of the cerebellar-thalamocortical circuit; 5. hyperactivation of limbic areas (amygdala, hippocampus, ventral striatum, septum, raphe, insula). These findings show remarkable similarities to imaging findings reported in PD patients. Exercise progressively improved motor deficits in lesioned rats, while increasing activation in dorsal striatum and rostral secondary motor cortex, attenuating a hyperemia of the zona incerta and eliciting a functional reorganization of regions participating in the cerebellar-thalamocortical circuit. Both lesions and exercise increased activation in mesolimbic areas (amygdala, hippocampus, ventral striatum, laterodorsal tegmental n., ventral pallidum), as well as in related paralimbic regions (septum, raphe, insula). Exercise, but not lesioning, resulted in decreases in rCBF in the medial prefrontal cortex (cingulate, prelimbic, infralimbic). Our results in this PD rat model uniquely highlight the breadth of functional reorganizations in motor and limbic circuits following lesion and long-term, aerobic exercise, and provide a framework for understanding the neural substrates underlying exercise-based neurorehabilitation.

Atp13a2-deficient mice exhibit neuronal ceroid lipofuscinosis, limited α-synuclein accumulation and age-dependent sensorimotor deficits

Mutations in ATP13A2 (PARK9), encoding a lysosomal P-type ATPase, are associated with both Kufor-Rakeb syndrome (KRS) and neuronal ceroid lipofuscinosis (NCL). KRS has recently been classified as a rare genetic form of Parkinson's disease (PD), whereas NCL is a lysosomal storage disorder. Although the transport activity of ATP13A2 has not been defined, in vitro studies show that its loss compromises lysosomal function, which in turn is thought to cause neuronal degeneration. To understand the role of ATP13A2 dysfunction in disease, we disrupted its gene in mice. Atp13a2(-/-) and Atp13a2(+/+) mice were tested behaviorally to assess sensorimotor and cognitive function at multiple ages. In the brain, lipofuscin accumulation, α-synuclein aggregation and dopaminergic pathology were measured. Behaviorally, Atp13a2(-/-) mice displayed late-onset sensorimotor deficits. Accelerated deposition of autofluorescent storage material (lipofuscin) was observed in the cerebellum and in neurons of the hippocampus and the cortex of Atp13a2(-/-) mice. Immunoblot analysis showed increased insoluble α-synuclein in the hippocampus, but not in the cortex or cerebellum. There was no change in the number of dopaminergic neurons in the substantia nigra or in striatal dopamine levels in aged Atp13a2(-/-) mice. These results show that the loss of Atp13a2 causes sensorimotor impairments, α-synuclein accumulation as occurs in PD and related synucleinopathies, and accumulation of lipofuscin deposits characteristic of NCL, thus providing the first direct demonstration that null mutations in Atp13a2 can cause pathological features of both diseases in the same organism.

Augmenting CNS glucocerebrosidase activity as a therapeutic strategy for parkinsonism and other Gaucher-related synucleinopathies

Mutations of GBA1, the gene encoding glucocerebrosidase, represent a common genetic risk factor for developing the synucleinopathies Parkinson disease (PD) and dementia with Lewy bodies. PD patients with or without GBA1 mutations also exhibit lower enzymatic levels of glucocerebrosidase in the central nervous system (CNS), suggesting a possible link between the enzyme and the development of the disease. Previously, we have shown that early treatment with glucocerebrosidase can modulate α-synuclein aggregation in a presymptomatic mouse model of Gaucher-related synucleinopathy (Gba1(D409V/D409V)) and ameliorate the associated cognitive deficit. To probe this link further, we have now evaluated the efficacy of augmenting glucocerebrosidase activity in the CNS of symptomatic Gba1(D409V/D409V) mice and in a transgenic mouse model overexpressing A53T α-synuclein. Adeno-associated virus-mediated expression of glucocerebrosidase in the CNS of symptomatic Gba1(D409V/D409V) mice completely corrected the aberrant accumulation of the toxic lipid glucosylsphingosine and reduced the levels of ubiquitin, tau, and proteinase K-resistant α-synuclein aggregates. Importantly, hippocampal expression of glucocerebrosidase in Gba1(D409V/D409V) mice (starting at 4 or 12 mo of age) also reversed their cognitive impairment when examined using a novel object recognition test. Correspondingly, overexpression of glucocerebrosidase in the CNS of A53T α-synuclein mice reduced the levels of soluble α-synuclein, suggesting that increasing the glycosidase activity can modulate α-synuclein processing and may modulate the progression of α-synucleinopathies. Hence, increasing glucocerebrosidase activity in the CNS represents a potential therapeutic strategy for GBA1-related and non-GBA1-associated synucleinopathies, including PD.

Resveratrol potentiates cytochrome P450 2 d22-mediated neuroprotection in maneb- and paraquat-induced parkinsonism in the mouse

A strong association between polymorphisms of the cytochrome P450 (CYP/Cyp) 2D6 gene and risk to Parkinson's disease (PD) is well established. The present study investigated the neuroprotective potential of Cyp2d22, a mouse ortholog of human CYP2D6, in maneb- and paraquat-induced parkinsonism and the mechanisms involved therein along with the effects of resveratrol on various parameters associated with Cyp2d22-mediated neuroprotection. The animals were treated intraperitoneally with resveratrol (10mg/kg, daily) and paraquat (10mg/kg) alone or in combination with maneb (30 mg/kg), twice a week, for 9 weeks, along with their respective controls. The subsets of animals were also treated intraperitoneally with a Cyp2d22 inhibitor, ketoconazole (100mg/kg, daily). Maneb and paraquat reduced Cyp2d22 and vesicular monoamine transporter type 2 (VMAT-2) expressions, the number of tyrosine hydroxylase-positive cells, and dopamine content and increased paraquat accumulation in the nigrostriatal tissues, oxidative stress, microglial activation, neuroinflammation, and apoptosis. Cyp2d22 inhibitor significantly exacerbated all these neurodegenerative indexes. Resveratrol cotreatment, partially but significantly, ameliorated the neurodegenerative changes by altering Cyp2d22 expression and paraquat accumulation. The results obtained in the study demonstrate that Cyp2d22 offers neuroprotection in maneb- and paraquat-induced dopaminergic neurodegeneration and resveratrol enhances its neuroprotective credentials by influencing Cyp2d22 expression and paraquat accumulation.

Inhibition of striatal soluble guanylyl cyclase-cGMP signaling reverses basal ganglia dysfunction and akinesia in experimental parkinsonism

OBJECTIVE

There is clearly a necessity to identify novel non-dopaminergic mechanisms as new therapeutic targets for Parkinson's disease (PD). Among these, the soluble guanylyl cyclase (sGC)-cGMP signaling cascade is emerging as a promising candidate for second messenger-based therapies for the amelioration of PD symptoms. In the present study, we examined the utility of the selective sGC inhibitor 1H-[1], [2], [4] oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ) for reversing basal ganglia dysfunction and akinesia in animal models of PD.

METHODS

The utility of the selective sGC inhibitor ODQ for reversing biochemical, electrophysiological, histochemical, and behavioral correlates of experimental PD was performed in 6-OHDA-lesioned rats and mice chronically treated with MPTP.

RESULTS

We found that one systemic administration of ODQ is sufficient to reverse the characteristic elevations in striatal cGMP levels, striatal output neuron activity, and metabolic activity in the subthalamic nucleus observed in 6-OHDA-lesioned rats. The latter outcome was reproduced after intrastriatal infusion of ODQ. Systemic administration of ODQ was also effective in improving deficits in forelimb akinesia induced by 6-OHDA and MPTP.

INTERPRETATION

Pharmacological inhibition of the sGC-cGMP signaling pathway is a promising non-dopaminergic treatment strategy for restoring basal ganglia dysfunction and attenuating motor symptoms associated with PD.

Aromatase and its inhibition in behaviour, obsessive compulsive disorder and parkinsonism

Oestrogens regulate normal behaviour and have been implicated in modulating pathological behaviour such as obsessive compulsive disorder and neurological disorder such as Parkinsonism. Therefore, by regulating the expression of the oestrogen-synthesising enzyme, aromatase, we may identify what behaviour is regulated by oestrogen. Inhibition of aromatase either genetically or pharmacologically has been reported to induce sexual behaviour impairment, compulsive behaviour and susceptibility to neurodegeneration.

Gaucher disease and parkinsonism, a molecular link theory

Mutant GBA was found recently to be the most prevalent risk factor for familial parkinsonism. The two diseases do not share common symptoms and there is no direct pathway to explain the mechanism by which GBA mutations can confer the risk. Increased burden on the degradative pathway caused by defective glucocerebrosidase, or toxic side effects of glycosylated lipids accumulation were proposed to explain brain damage. Both hypotheses are not sufficient to explain the linkage. In order to develop a more inclusive theory we introduced into the model the prion theory and the second hit. Other possibilities are also brought into consideration.

Catalytic function of PLA2G6 is impaired by mutations associated with infantile neuroaxonal dystrophy but not dystonia-parkinsonism

BACKGROUND

Mutations in the PLA2G6 gene have been identified in autosomal recessive neurodegenerative diseases classified as infantile neuroaxonal dystrophy (INAD), neurodegeneration with brain iron accumulation (NBIA), and dystonia-parkinsonism. These clinical syndromes display two significantly different disease phenotypes. NBIA and INAD are very similar, involving widespread neurodegeneration that begins within the first 1-2 years of life. In contrast, patients with dystonia-parkinsonism present with a parkinsonian movement disorder beginning at 15 to 30 years of age. The PLA2G6 gene encodes the PLA2G6 enzyme, also known as group VIA calcium-independent phospholipase A(2), which has previously been shown to hydrolyze the sn-2 acyl chain of phospholipids, generating free fatty acids and lysophospholipids.

METHODOLOGY/PRINCIPAL FINDINGS

We produced purified recombinant wildtype (WT) and mutant human PLA2G6 proteins and examined their catalytic function using in vitro assays with radiolabeled lipid substrates. We find that human PLA2G6 enzyme hydrolyzes both phospholipids and lysophospholipids, releasing free fatty acids. Mutations associated with different disease phenotypes have different effects on catalytic activity. Mutations associated with INAD/NBIA cause loss of enzyme activity, with mutant proteins exhibiting less than 20% of the specific activity of WT protein in both lysophospholipase and phospholipase assays. In contrast, mutations associated with dystonia-parkinsonism do not impair catalytic activity, and two mutations produce a significant increase in specific activity for phospholipid but not lysophospholipid substrates.

CONCLUSIONS/SIGNIFICANCE

These results indicate that different alterations in PLA2G6 function produce the different disease phenotypes of NBIA/INAD and dystonia-parkinsonism. INAD/NBIA is caused by loss of the ability of PLA2G6 to catalyze fatty acid release from phospholipids, which predicts accumulation of PLA2G6 phospholipid substrates and provides a mechanistic explanation for the accumulation of membranes in neuroaxonal spheroids previously observed in histopathological studies of INAD/NBIA. In contrast, dystonia-parkinsonism mutations do not appear to directly impair catalytic function, but may modify substrate preferences or regulatory mechanisms for PLA2G6.

Biochemical alterations of the striatum in an MPTP-treated mouse model of Parkinson's disease

We investigated the biochemical alterations of the striatum of mice subjected to seven experimental schedules with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride (MPTP) treatment. The mice were treated intraperitoneally (i.p.) with MPTP (20 mg/kg in saline) four times a day at 2-hr intervals showed severe and persistent depletions of dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the striatum, as compared with those (1) treated with MPTP (15 mg/kg in saline, i.p.) once a day for 14 consecutive days; (2)MPTP (30 mg/kg in saline, i.p.) twice a day for 5 consecutive days; (3) MPTP (10 mg/kg in saline, i.p.) four times a day at 1-hr intervals for 2 consecutive days; (4) MPTP (20 mg/kg in saline, i.p.) once a day for 4 consecutive days; (5) MPTP (20 mg/kg in saline, i.p.) twice a day for 2 consecutive days; (6) MPTP (20 mg/kg in saline, i.p.) twice a day for 4 consecutive days. In our Western blot analysis, furthermore, the mice that received MPTP (20 mg/kg in saline) four times a day at 2-hr intervals showed a severe decrease of the striatal tyrosine hydroxylase (TH) protein levels and a significant increase of the striatal glial fibrillary acidic protein (GFAP) levels. These results demonstrate that the model with acute MPTP treatment can cause severe neuronal damage in the mouse striatum, as compared to the model with continuous treatment with MPTP. Thus our findings may support the validity of acute MPTP treatment model for unraveling in the neurodegenerative processes in PD.

Differential interaction of the E3 ligase parkin with the proteasomal subunit S5a and the endocytic protein Eps15

Parkin is a multidomain E3 ligase associated with autosomal recessive Parkinson disease. The N-terminal ubiquitin-like domain (Ubld) of parkin functions with the S5a proteasomal subunit, positioning substrate proteins for degradation. In addition the parkin Ubld recruits the endocytotic protein Eps15, allowing the E3 ligase to ubiquinate Eps15 distal from its parkin-interacting site. The recognition sequences in the S5a subunit and Eps15 for the parkin Ubld are ubiquitin-interacting motifs (UIM). Each protein has two UIM sequences separated by a 50-residue spacer in S5a, but only approximately 5 residues in Eps15. In this work we used NMR spectroscopy to determine how the parkin Ubld recognizes the proteasomal subunit S5a compared with Eps15, a substrate for ubiquitination. We show that Eps15 contains two flexible alpha-helices each encompassing a UIM sequence. The alpha-helix surrounding UIM II is longer than that for UIM I, a situation that is reversed from S5a. Furthermore, we show the parkin Ubld preferentially binds to UIM I in the S5a subunit. This interaction is strongly diminished in a K48A substitution, found near the center of the S5a interacting surface on the parkin Ubld. In contrast to S5a, parkin recruits Eps15 using both its UIM sequences resulting in a larger interaction surface that includes residues from beta1 and beta2, not typically known to interact with UIM sequences. These results show that the parkin Ubld uses differential surfaces to recruit UIM regions from the S5a proteasomal subunit compared with Eps15 involved in cell signaling.

Neuronal NOS and cyclooxygenase-2 contribute to DNA damage in a mouse model of Parkinson disease

DNA damage is a proposed pathogenic factor in neurodegenerative disorders such as Parkinson disease. To probe the underpinning mechanism of such neuronal perturbation, we sought to produce an experimental model of DNA damage. We thus first assessed DNA damage by in situ nick translation and emulsion autoradiography in the mouse brain after administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP; 4 x 20 mg/kg, ip, every 2 h), a neurotoxin known to produce a model of Parkinson disease. Here we show that DNA strand breaks occur in vivo in this mouse model of Parkinson disease with kinetics and a topography that parallel the degeneration of substantia nigra neurons, as assessed by FluoroJade labeling. Previously, nitric oxide synthase and cyclooxygenase-2 (Cox-2) were found to modulate MPTP-induced dopaminergic neuronal death. We thus assessed the contribution of these enzymes to DNA damage in mice lacking neuronal nitric oxide synthase (nNOS), inducible nitric oxide synthase (iNOS), or Cox-2. We found that the lack of Cox-2 and nNOS activities but not of iNOS activity attenuated MPTP-related DNA damage. We also found that not only nuclear, but also mitochondrial, DNA is a target for the MPTP insult. These results suggest that the loss of genomic integrity can be triggered by the concerted actions of nNOS and Cox-2 and provide further support to the view that DNA damage may contribute to the neurodegenerative process in Parkinson disease.

PINK1-associated Parkinson's disease is caused by neuronal vulnerability to calcium-induced cell death

Mutations in PINK1 cause autosomal recessive Parkinson's disease. PINK1 is a mitochondrial kinase of unknown function. We investigated calcium homeostasis and mitochondrial function in PINK1-deficient mammalian neurons. We demonstrate physiologically that PINK1 regulates calcium efflux from the mitochondria via the mitochondrial Na(+)/Ca(2+) exchanger. PINK1 deficiency causes mitochondrial accumulation of calcium, resulting in mitochondrial calcium overload. We show that calcium overload stimulates reactive oxygen species (ROS) production via NADPH oxidase. ROS production inhibits the glucose transporter, reducing substrate delivery and causing impaired respiration. We demonstrate that impaired respiration may be restored by provision of mitochondrial complex I and II substrates. Taken together, reduced mitochondrial calcium capacity and increased ROS lower the threshold of opening of the mitochondrial permeability transition pore (mPTP) such that physiological calcium stimuli become sufficient to induce mPTP opening in PINK1-deficient cells. Our findings propose a mechanism by which PINK1 dysfunction renders neurons vulnerable to cell death.

Excessive S-adenosyl-L-methionine-dependent methylation increases levels of methanol, formaldehyde and formic acid in rat brain striatal homogenates: possible role in S-adenosyl-L-methionine-induced Parkinson's disease-like disorders

AIMS

Excessive methylation may be a precipitating factor for Parkinson's disease (PD) since S-adenosylmethionine (SAM), the endogenous methyl donor, induces PD-like changes when injected into the rat brain. The hydrolysis of the methyl ester bond of the methylated proteins produces methanol. Since methanol is oxidized into formaldehyde, and formaldehyde into formic acid in the body, we investigated the effects of SAM on the production of methanol, formaldehyde and formic acid in rat brain striatal homogenates and the toxicity of these products in PC12 cells.

MAIN METHODS

Radio-enzymatic and colorimetric assays, cell viability, Western blot.

KEY FINDINGS

SAM increased the formation of methanol, formaldehyde and formic acid in a concentration and time-dependent manner. Concentrations of [3H-methyl]-SAM at 0.17, 0.33, 0.67 and 1.34 nM produced 3.8, 8.0, 18.3 and 34.4 fmol/mg protein/h of [3H] methanol in rat striatal homogenates, respectively. SAM also significantly generated formaldehyde and formic acid in striatal homogenates. Formaldehyde was the most toxic metabolite to differentiated PC12 pheochromocytoma cells in cell culture studies, indicating that formaldehyde formed endogenously may contribute to neuronal damage in excessive methylation conditions. Subtoxic concentration of formaldehyde decreased the expression of tyrosine hydroxylase, the limiting factor in dopamine synthesis. Formaldehyde was more toxic to catecholaminergic PC12 cells than C6 glioma cells, indicating that neurons are more vulnerable to formaldehyde than glia cells.

SIGNIFICANCE

We suggest that excessive carboxylmethylation of proteins might be involved in the SAM-induced PD-like changes and in the aging process via the toxic effects of formaldehyde.

Coexistence of mutations in PINK1 and mitochondrial DNA in early onset parkinsonism

AIMS AND BACKGROUND

Various genes have been identified for monogenic disorders resembling Parkinson's disease. The products of some of these genes are associated with mitochondria and have been implicated in cellular protection against oxidative damage. In the present study we analysed fibroblasts from a patient carrying the homozygous mutation p.W437X in the PTEN-induced kinase 1 (PINK1), which manifested a very early onset parkinsonism.

RESULTS

Patient's fibroblasts did not show variation in the mtDNA copy number or in the expression of the oxidative phosphorylation complexes. Sequence analysis of the patient's mtDNA presented two new missense mutations in the ND5 (m.12397A>G, p.T21A) and ND6 (m. 14319T>C, p.N119D) genes coding for two subunits of complex I. The two mutations were homoplasmic in both the patient and the patient's mother. Patient's fibroblasts resulted in enhanced constitutive production of the superoxide anion radical that was abrogated by inhibitor of the complex I. Moreover enzyme kinetic analysis of the NADH:ubiquinone oxidoreductase showed changes in the substrates affinity.

CONCLUSION

To our knowledge, this is the first report showing co-segregation of a Parkinson's disease related nuclear gene mutation with mtDNA mutation(s). Our observation might shed light on the clinical heterogeneity of the hereditary cases of Parkinson's disease, highlighting the hitherto unappreciated impact of coexisting mtDNA mutations in determining the development and the clinical course of the disease.

Failure of acute administration with proteasome inhibitor to provide a model of Parkinson's disease in mice

We investigated to determine whether acute administration of proteasome inhibitor can cause dopaminergic cell loss in mice, in comparison with that of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). The four intraperitoneally administrations of MPTP at 1-h intervals to mice decreased significantly the concentration of dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the striatum after 5 days, in comparison with vehicle-treated animals. In contrast, the three subcutaneously administrations of carbobenzoxy-L-gamma-t-butyl-L-glutamyl-L-alanyl-L-leucinal (PSI) did not show significant changes in the concentration of dopamine, DOPAC and HVA in the striatum after 5 days, in comparison with vehicle-treated animals. Our Western blot analysis also showed that the four administrations of MPTP at 1-h intervals to mice produced a significant reduction of anti-tyrosine hydroxylase antibody (TH) protein levels in the striatum after 5 days after. In PSI-treated mice. In contrast, no significant change of TH protein levels was observed in the striatum 5 days after the final treatment with PSI. Furthermore, a significant decrease of TH protein levels was observed in the striatum of MPTP-treated mice, as compared with PSI-treated animals. The present study demonstrates that the acute treatment with proteasome inhibitor PSI did not cause the dopaminergic neurotoxicity in mice, as compared with acute treatment with MPTP. Thus, our findings suggest that acute proteasome inhibition is not a reliable model for Parkinson's disease.

[The Na+,K+ pump continues to cause surprise]

This article provides an overview of news about the Na+,K+ pump, an indispensable enzyme whose protein structure has been described in a recent article in Nature, 50 years after its discovery. In combination with mutational analysis, the structure reveals the binding pocket for the K+ ions and the regulation of Na+ transport by a strategically located C-terminus of the protein. Focus is also on the pathophysiology of two neurological disorders, familial hemiplegic migraine and rapid-onset dystonia-parkinsonism, recently shown to be caused by mutations in the Na+,K+-ATPase.

Results From a 2-Year Centralized Tolcapone Liver Enzyme Monitoring Program

OBJECTIVES

Tolcapone, administered with levodopa/carbidopa to patients with Parkinson disease, is an effective and generally well-tolerated adjunctive therapy. However, 4 early cases of hepatotoxicity causing 3 deaths in patients not properly monitored gave rise to more rigorous liver function test monitoring guidelines and a liver function test monitoring program in which blood samples from tolcapone-treated patients were tested and results were collected in a central database. We analyzed these results to determine the percentages of patients with at least 1 aspartate aminotransferase (AST) or alanine aminotransferase (ALT) elevation above the upper limit of normal (ULN) and at least 1 elevation greater than 2 times the ULN.

METHODS

This retrospective, observational analysis included all AST and ALT values recorded in the database from 11,883 samples from patients who received tolcapone for up to 2 years or longer (January 1999-January 2001).

RESULTS

Of 1725 patients who had at least 1 AST or ALT measurement, 3.9% (n = 67) had elevations above the ULN. Less than 1% (15/1725) of patients had AST or ALT elevations greater than 2 times the ULN. Most values returned to normal during continued tolcapone treatment. In 472 patients monitored biweekly while receiving tolcapone for 20 to 114 consecutive weeks, only 0.6% (n = 3) had an AST or ALT value greater than 2 times the ULN; no significant elevations occurred in the remaining 469 (99.4%).

CONCLUSIONS

This analysis of results from the central monitoring program suggests that significant transaminase elevations are rare, typically transient, and may return to normal in the face of continued tolcapone therapy in most patients.

Familial parkinsonism and ophthalmoplegia from a mutation in the mitochondrial DNA helicase twinkle

OBJECTIVE

To describe the clinical phenotype and genetic basis of a family with autosomal dominant progressive external ophthalmoplegia and parkinsonism from a Twinkle mutation.

DESIGN

All coding exons of POLG1, Twinkle (aka C10ORF2, PEO1), and ANT1 (SLC25A4) were sequenced in the proband with targeted sequencing of the Twinkle gene in all additional subjects.

SUBJECTS

Members of a 3-generation family followed up in a neuromuscular disease center for dominantly inherited progressive external ophthalmoplegia.

RESULTS

We identified a heterozygous G1121A mutation (R374Q) in exon 1 of Twinkle that segregated with the disease phenotype in all affected family members. No pathogenic mutations were present in POLG1 or ANT1.

CONCLUSION

This finding broadens the clinical spectrum of Twinkle gene mutations and further implicates loss of mitochondrial DNA integrity in the pathogenesis of Parkinson disease.

A macrophage-nanozyme delivery system for Parkinson's disease

Selective delivery of antioxidants to the substantia nigra pars compacta (SNpc) during Parkinson's disease (PD) can potentially attenuate oxidative stress and as such increase survival of dopaminergic neurons. To this end, we developed a bone-marrow-derived macrophage (BMM) system to deliver catalase to PD-affected brain regions in an animal model of human disease. To preclude BMM-mediated enzyme degradation, catalase was packaged into a block ionomer complex with a cationic block copolymer, polyethyleneimine-poly(ethylene glycol) (PEI-PEG). The self-assembled catalase/PEI-PEG complexes, "nanozymes", were ca. 60 to 100 nm in size, stable in pH and ionic strength, and retained antioxidant activities. Cytotoxicity was negligible over a range of physiologic nanozyme concentrations. Nanozyme particles were rapidly, 40-60 min, taken up by BMM, retained catalytic activity, and released in active form for greater than 24 h. In contrast, "naked" catalase was rapidly degraded. The released enzyme decomposed microglial hydrogen peroxide following nitrated alpha-synuclein or tumor necrosis factor alpha activation. Following adoptive transfer of nanozyme-loaded BMM to 1-methyl 4-phenyl 1,2,3,6-tetrahydropyridine-intoxicated mice, ca. 0.6% of the injected dose were found in brain. We conclude that cell-mediated delivery of nanozymes can reduce oxidative stress in laboratory and animal models of PD.

The DNA polymerase gamma Y955C disease variant associated with PEO and parkinsonism mediates the incorporation and translesion synthesis opposite 7,8-dihydro-8-oxo-2'-deoxyguanosine

Mitochondrial DNA is replicated and repaired by DNA polymerase gamma (pol gamma), encoded by the POLG gene. The Y955C substitution in POLG leads to autosomal dominant progressive external ophthalmoplegia (PEO) with other severe phenotypes. PEO patients with this mutation can further develop parkinsonism or premature ovarian failure. Mouse and yeast models with this mutation show enhanced amounts of oxidative lesions and increased mtDNA damage. In DNA pol gamma, Tyr955 plays a critical role in catalysis and high fidelity DNA synthesis. 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-oxo-dG) is one of the most common oxidative lesions in DNA and can promote transversion mutations. Mitochondria are thought to be a major source of endogenous reactive oxygen species that can react with dG to form 8-oxo-dG as one of the more common products. DNA polymerases can mitigate mutagenesis by 8-oxo-dG through allosteric interactions from amino acid side chains, which limit the anti-conformation of the 8-oxo-dG template base during translesion DNA synthesis. Here, we show that the Y955C pol gamma displays relaxed discrimination when either incorporating 8-oxo-dGTP or translesion synthesis opposite 8-oxo-dG. Molecular modeling and biochemical analysis suggest that this residue, Tyr955, in conjunction with Phe961 helps attenuate the anti-conformation in human pol gamma for error free bypass of 8-oxo-dG and substitution to Cys allows the mutagenic syn conformation. Collectively, these results offer a biochemical link between the observed oxidative stress in model systems and parkinsonism in patients, suggesting that patients harboring the Y955C POLG mutation may undergo enhanced oxidative stress and DNA mutagenesis.

Response to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) differs in mouse strains and reveals a divergence in JNK signaling and COX-2 induction prior to loss of neurons in the substantia nigra pars compacta

Parkinson's disease (PD) is a neurodegenerative disease whose hallmark pathological features include a selective loss of dopaminergic neurons in the midbrain. Recent studies have described the activation of a stress-induced signal cascade, c-Jun N-terminal kinase (JNK)-mediated activation of c-Jun, and an increase in the expression of a downstream effector, cyclooxygenase 2 (COX-2), in postmortem PD brains. The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which induces selective neuronal loss in the midbrain similar to that seen in PD, also induces JNK-mediated activation of c-Jun and generates a COX-2 response in C57BL/6J mice. However, mice exhibit a strain-dependent susceptibility to MPTP. Identifying the point(s) of molecular divergence in the MPTP-induced response may provide insight into the cause of PD or a means to identify susceptibility to PD in humans. Here we examined JNK signaling and COX-2 induction in two strains of mice, the MPTP-sensitive C57BL/6J and the MPTP-resistant Swiss Webster (SW). We show that C57BL/6J and SW strains differ in JNK and c-Jun activation in response to MPTP. In addition, the MPTP-induced COX-2 response occurs exclusively in C57BL/6J mice. Furthermore, strain-specific responses to MPTP are not due to differences in MPP(+) levels and are not secondary to cell death. These results provide evidence toward a mechanism of strain-dependent sensitivity to MPTP.

17β-Estradiol reduces nitrotyrosine immunoreactivity and increases SOD1 and SOD2 immunoreactivity in nigral neurons in male mice following MPTP insult

Emerging evidence suggests the beneficial effects of estrogen on Parkinson's disease (PD), yet the mechanisms of action implicated remain elusive. While experimental evidence suggests that estrogen possesses potent antioxidative properties, it is still unknown whether the hormone exhibits a neuroprotection in a PD animal model through its antioxidant activities. This study therefore investigated the effects of 17beta-estradiol (E2) on the immunoreactivity of nigral neurons and glia for nitrotyrosine (NT, a stable marker for oxidative stress), Cu/Zn superoxide dismutase (SOD1) and Mn superoxide dismutase (SOD2) in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model. Adult male mice were treated with E2 or vehicle for 11 days during which they were injected with MPTP or saline on the sixth day. The brains were collected on day 11 and quantitative immunohistochemistry was used to assess the number of NT-, SOD1- and SOD2-immunoreactive (IR) cells in the substantia nigra pars compacta (SNpc). In saline-treated group, E2 decreased NT-IR neuronal number and raised SOD1 and SOD2 expression in neurons and glia in the SNpc. MPTP induced a significant increase in the number of NT- and SOD2-IR neurons, but decreased the number of SOD1-IR neurons. MPTP also triggered a significant increase of SOD2- and SOD1-IR glial number. E2 pretreatment in MPTP mice reduced the number of NT-IR neurons, increased the number of SOD1- and SOD2-IR neurons, but did not alter the MPTP effect on glia immunoreactive to either SOD. Stimulation of SOD1 and SOD2 expression in nigral neurons suggests that E2 provides neuroprotection against MPTP-induced oxidative stress, partly through its ability to act as an antioxidant.

Localization of Parkinson’s disease-associated LRRK2 in normal and pathological human brain

Mutations in the LRRK2 gene cause autosomal dominant, late-onset parkinsonism, which presents with pleomorphic pathology including alpha-synucleopathy. To promote our understanding of the biological role of LRRK2 in the brain we examined the distribution of LRRK2 mRNA and protein in postmortem human brain tissue from normal and neuropathological subjects. In situ hybridization and immunohistochemical analysis demonstrate the expression and localization of LRRK2 to various neuronal populations in brain regions implicated in Parkinson's disease (PD) including the cerebral cortex, caudate-putamen and substantia nigra pars compacta. Immunofluorescent double labeling studies additionally reveal the prominent localization of LRRK2 to cholinergic-, calretinin- and GABA(B) receptor 1-positive, dopamine-innervated, neuronal subtypes in the caudate-putamen. The distribution of LRRK2 in brain tissue from sporadic PD and dementia with Lewy bodies (DLB) subjects was also examined. In PD brains, LRRK2 immunoreactivity localized to nigral neuronal processes is dramatically reduced which reflects the disease-associated loss of dopaminergic neurons in this region. However, surviving nigral neurons occasionally exhibit LRRK2 immunostaining of the halo structure of Lewy bodies. Moreover, LRRK2 immunoreactivity is not associated with Lewy neurites or with cortical Lewy bodies in sporadic PD and DLB brains. These observations indicate that LRRK2 is not a primary component of Lewy bodies and does not co-localize with mature fibrillar alpha-synuclein to a significant extent. The localization of LRRK2 to key neuronal populations throughout the nigrostriatal dopaminergic pathway is consistent with the involvement of LRRK2 in the molecular pathogenesis of familial and sporadic parkinsonism.

Modification of L-DOPA pharmacological activity by MAO inhibitors

Dopamine behaves mainly as a MAO-A substrate in rodent brain, but selective inhibition of MAO-B results in an increased turning activity following L-DOPA administration in hemi-Parkinsonian rodents. Unilateral substantia nigra dopaminergic denervation results in serotonergic hyper-innervation which may increase the contribution of MAO-A in the denervated striatum. Possibly as a result of this, there was no change in striatal MAO-A activity when 95% of dopaminergic innervation was reduced by 6-hydroxydopamine, as assessed by apomorphine-induced turning activity. MAO-B as well as MAO-A may contribute to deamination of dopamine produced from L-DOPA.

GSTpi expression mediates dopaminergic neuron sensitivity in experimental parkinsonism

The cause of 95% of Parkinson's disease (PD) cases is unknown. It is hypothesized that PD arises from an interaction of free-radical-generating agents with an underlying genetic susceptibility to these compounds. Here we use the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine model of parkinsonism to examine the role of a dual function protein, GSTpi, in dopaminergic neuron death. GSTpi is the only GST family member expressed in substantia nigra neurons. GSTpi reduction by pharmacological blockade, RNA inhibition, and gene targeting increases sensitivity to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, suggesting that differential expression of GSTpi contributes to the sensitivity to xenobiotics in the substantia nigra and may influence the pathogenesis of reactive oxygen species-induced neurological disorders including PD.

Different parkinsonism models produce a time-dependent induction of COX-2 in the substantia nigra of rats

The present study investigated the effects on general activity, COX-2 and TH protein expression of intranigral neurotoxins LPS, MPTP or 6-OHDA infusion in rats. Results indicate that LPS produced an increase in locomotion frequency (3 and 7 days after surgery) and a strong up-regulation of COX-2 protein 16 and 24 h after surgery, as observed in the substantia nigra (SN). The MPTP model generated impairment in locomotion frequency 24 h after surgery. Besides, MPTP caused a marked up-regulation in COX-2 protein observed in the SN 16 h after surgery. Moreover, the 6-OHDA model produced severe motor impairment indicated by the decrease in locomotion (24 h) and rearing (24 h, 3 and 7 days) frequencies and also an increase in latency (24 h, 3 and 7 days) and immobility (24 h and 3 days) times. We also demonstrated an up-regulation of COX-2, which occurred in the SN 4-24 h after surgery. TH protein did not appear to be reduced in the striatum in the groups lesioned with the neurotoxins. In contrast, the TH content of SN was significantly reduced in the groups lesioned with the very same neurotoxins. For all the models analyzed, we observed no statistical differences in the expression of COX-2 in the striatum along the time-points. The results of the present study suggest that COX-2 induction patterns differ in function of the neurotoxin tested. Such time-dependent induction has been found to be relatively constant, a fact of great significance considering the importance of the neuroinflammatory process in Parkinson's disease.

Alterations of the expression and activity of midbrain nitric oxide synthase and soluble guanylyl cyclase in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced Parkinsonism in mice

The study was aimed at investigating the expression and the activity of neuronal nitric oxide synthase, and of soluble guanylyl cyclase and phosphodiesterase activities that regulate guanosine 3',5'-cyclic monophosphate level in the midbrain, in a mouse model of PD using 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine injections. Adult male mice of the C57/BL strain were given three i.p. injections of physiological saline or three i.p. injections of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine solution in physiological saline at 2 h intervals (summary 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine dose: 40 mg/kg), and were killed 3, 7, or 14 days later. mRNA, protein level, and/or activities of neuronal nitric oxide synthase, soluble guanylyl cyclase, phosphodiesterase and guanosine 3',5'-cyclic monophosphate were determined. Immunohistochemistry showed about 75% decrease in the number of tyrosine hydroxylase-positive neurons in the substantia nigra pars compacta. Mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine showed increased midbrain guanylyl cyclase and total nitric oxide synthase activities at 3, 7, and 14 days post-treatment. The specific neuronal nitric oxide synthase inhibitor 7-nitroindazole (10 microM) and the specific inducible nitric oxide synthase inhibitor 1400W (10 microM) inhibited the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced excess in nitric oxide synthase activity by 63-70 and 13-25%, respectively. The increases in total midbrain nitric oxide synthase activity were accompanied by elevated guanosine 3',5'-cyclic monophosphate, enhanced expression of neuronal nitric oxide synthase and of the beta1 subunit of guanylyl cyclase at both mRNA and protein levels that persisted up to the end of the observation period, and by enhanced neuronal nitric oxide synthase and guanylyl cyclase beta1 immunoreactivities in substantia nigra pars compacta 7 and 14 days after the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine treatment. The increases in guanylyl cyclase activity were found to occur exclusively due to increased maximal enzyme activity. No 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced change in phosphodiesterase activity has been detected in any brain region studied. 7-Nitroindazole prevented a significant increase in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced midbrain guanosine 3',5'-cyclic monophosphate level and neurodegeneration of dopaminergic neurons. These results raise the possibility that the nitric oxide/guanylyl cyclase/guanosine 3',5'-cyclic monophosphate signaling pathway may play a role in maintaining dopaminergic neurons function in substantia nigra pars compacta.

Mutations Phe785Leu and Thr618Met in Na+,K+-ATPase, associated with familial rapid-onset dystonia parkinsonism, interfere with Na+ interaction by distinct mechanisms

The Na(+),K(+)-ATPase plays key roles in brain function. Recently, missense mutations in the Na(+),K(+)-ATPase were found associated with familial rapid-onset dystonia parkinsonism (FRDP). Here, we have characterized the functional consequences of FRDP mutations Phe785Leu and Thr618Met. Both mutations lead to functionally altered, but active, Na(+),K(+)-pumps, that display reduced apparent affinity for cytoplasmic Na(+), but the underlying mechanism differs between the mutants. In Phe785Leu, the interaction of the E(1) form with Na(+) is defective, and the E(1)-E(2) equilibrium is not displaced. In Thr618Met, the Na(+) affinity is reduced because of displacement of the conformational equilibrium in favor of the K(+)-occluded E(2)(K(2)) form. In both mutants, K(+) interaction at the external activating sites of the E(2)P phosphoenzyme is normal. The change of cellular Na(+) homeostasis is likely a major factor contributing to the development of FRDP in patients carrying the Phe785Leu or Thr618Met mutation. Phe785Leu moreover interferes with Na(+) interaction on the extracellular side and reduces the affinity for ouabain significantly. Analysis of two additional Phe(785) mutants, Phe785Leu/Leu786Phe and Phe785Tyr, demonstrated that the aromatic function of the side chain, as well as its exact position, is critical for Na(+) and ouabain binding. The effects of substituting Phe(785) could be explained by structural modeling, demonstrating that Phe(785) participates in a hydrophobic network between three transmembrane segments. Thr(618) is located in the cytoplasmic part of the molecule near the catalytic site, and the structural modeling indicates that the Thr618Met mutation interferes with the bonding pattern in the catalytic site in the E(1) form, thereby destabilizing E(1) relative to E(2)(K(2)).

Identification of the protein disulfide isomerase family member PDIp in experimental Parkinson's disease and Lewy body pathology

Parkinson's disease (PD) is a slowly progressing neurodegenerative disorder with no clear etiology. Pathological hallmarks of the disease include the loss of dopaminergic neurons from the substantia nigra (SN) and the presence of Lewy bodies (LBs) (alpha-synuclein and ubiquitin-positive, eosinophilic, cytoplasmic inclusions) in many of the surviving neurons. Experimental modeling of PD neurodegeneration using the neurotoxins 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and 1-methyl-4-phenyl-pyridinium (MPP(+)) has identified changes in gene expression of different endoplasmic reticulum (ER) stress proteins associated with MPTP- and PD-related neurodegeneration. We show that the protein disulfide isomerase (PDI) family member pancreatic protein disulfide isomerase (PDIp), previously considered exclusively expressed in pancreatic tissue, is uniquely upregulated among PDI family members within 24 h following exposure of retinoic acid (RA)-differentiated SH-SY5Y human neuroblastoma cells to either 1 mM MPP(+) or 10 microM of the highly specific proteasome inhibitor lactacystin. RT-PCR confirms PDIp expression in brain of post-mortem human PD subjects and immunohistochemical studies demonstrate PDIp immunoreactivity in LBs. Collectively, these findings suggest that increased PDIp expression in dopaminergic (DA) neurons might contribute to LB formation and neurodegeneration, and that this increased PDIp expression may be the result of proteasome impairment.

Ablation of the inflammatory enzyme myeloperoxidase mitigates features of Parkinson's disease in mice

Parkinson's disease (PD) is characterized by a loss of ventral midbrain dopaminergic neurons, which can be modeled by the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Inflammatory oxidants have emerged as key contributors to PD- and MPTP-related neurodegeneration. Here, we show that myeloperoxidase (MPO), a key oxidant-producing enzyme during inflammation, is upregulated in the ventral midbrain of human PD and MPTP mice. We also show that ventral midbrain dopaminergic neurons of mutant mice deficient in MPO are more resistant to MPTP-induced cytotoxicity than their wild-type littermates. Supporting the oxidative damaging role of MPO in this PD model are the demonstrations that MPO-specific biomarkers 3-chlorotyrosine and hypochlorous acid-modified proteins increase in the brains of MPTP-injected mice. This study demonstrates that MPO participates in the MPTP neurotoxic process and suggests that inhibitors of MPO may provide a protective benefit in PD.

White matter hyperintensities and cortical acetylcholinesterase activity in parkinsonian dementia

OBJECTIVE

To investigate the relationship between the severity of white matter hyperintensities (WMH) and cortical acetylcholinesterase (AChE) activity in parkinsonian dementia (PDem).

METHODS

PDem (n = 11) and control subjects (n = 14) underwent [11C]methyl-4-piperidinyl propionate (11C-PMP) AChE brain positron emission tomography and magnetic resonance (MR) imaging. Presence of WMH on proton density and T2 MR images was scored using a modified version of the semi-quantitative rating scale by Scheltens et al. [J Neurol Sci114 (1993)].

RESULTS

Analysis demonstrated significantly lower mean cortical (11)C-PMP k3 hydrolysis rates in PDem (-19.9%) when compared with control subjects (P < 0.0001). PDem subjects had higher mean severity of WMH (+20.1%) when compared with control subjects (P < 0.05). When WMH severity was entered into the analysis of variance model, there was no significant co-variate effect on cortical AChE activity (F = 0.24, ns).

CONCLUSIONS

The concomitant presence of mild to moderate WMH in patients with PDem does not have a significant effect on cortical AChE activity.

Activation of mitochondrial ATP-sensitive potassium channels improves rotenone-related motor and neurochemical alterations in rats

Our previous studies revealed that activation of mitochondrial ATP-sensitive potassium channels exerted protective effects on rotenone-treated rats and cultured cells. The aim of the present study is to examine the potential therapeutic effects of iptakalim, an ATP-sensitive potassium-channel opener, and diazoxide, a selective mitochondrial ATP-sensitive potassium-channel opener, on Parkinsonian symptoms in rats induced by rotenone. Rats were treated with rotenone (2.5 mg/kg s.c.) daily for 4 wk. This treatment caused a depletion of dopamine in the striatum and substantia nigra. Behaviourally, rotenone-infused rats exhibit Parkinsonian symptoms. Catalepsy was estimated by a 9-cm bar test. Treatment with L-dopa (10 mg/kg.d p.o.), iptakalim (0.75, 1.5, 3.0 mg/kg.d p.o.) and diazoxide (3.0 mg/kg.d p.o.) for 2 wk improved behavioural dysfunction and elevated dopamine contents in the striatum and substantia nigra of rotenone-treated rats. Studies also found that iptakalim and diazoxide could reduce the enzymic activities and mRNA levels of inducible nitric oxide synthase elicited by chronic administration of rotenone. All neurorestorative effects by both iptakalim and diazoxide were abolished by 5-hydroxydecanoate, a selective mitochondrial ATP-sensitive potassium-channel blocker. Collectively, the data suggested that mitochondrial ATP-sensitive potassium channels play a key role in improving both Parkinsonian symptoms and neurochemistry alterations of rotenone model rats, and selective activation of mitochondrial ATP-sensitive potassium channels may provide a new therapeutic strategy for treatment of early Parkinson's disease.

Effects of pallidotomy on motor symptoms in an animal model of Parkinson's disease

The present study was designed to evaluate the motor effects of lesioning the internal globus pallidus in an animal model of Parkinson's disease. Fourty rats were divided into four groups (each of 10 rats) which received either unilateral 6-hydroxydopamine (6-OHDA) lesions of the medial forebrain bundle (mfb) plus sham surgery to the pallidum, sham surgery of mfb plus N-methyl-D-aspartate (NMDA) induced pallidal lesions, combined 6-OHDA mfb + NMDA pallidal lesions or sham surgery to both structures. Animals with 6-OHDA lesions developed significant ipsilateral biases in head position, body axis and circling after amphetamine challenge (all P < 0.05). Prominent contralateral deficits were present in sensorimotor response latency and contralateral circling was induced by apomorphine challenge (both P < 0.05). The addition of an NMDA pallidal lesion, improved the head position and body axis biases, as well as dopamine-agonist induced rotation and contralateral reaction time in a sensorimotor task (all P < 0.05). There was, however, a slight worsening of sensorimotor response on the ipsilateral side (P < 0.05). Pallidal lesions in the absence of 6-OHDA lesions produced contralateral head position and body axis biases (both P < 0.05). These data indicate that pallidotomy improves some, but not all aspects of parkinsonian motor dysfunction in an animal model of Parkinson's disease (PD).

MTH1, an oxidized purine nucleoside triphosphatase, protects the dopamine neurons from oxidative damage in nucleic acids caused by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine

We previously reported that 8-oxoguanine (8-oxoG) accumulates in the cytoplasm of dopamine neurons in the substantia nigra of patients with Parkinson's disease and the expression of MTH1 carrying an oxidized purine nucleoside triphosphatase activity increases in these neurons, thus suggesting that oxidative damage in nucleic acids is involved in dopamine neuron loss. In the present study, we found that levels of 8-oxoG in cellular DNA and RNA increased in the mouse nigrostriatal system during the tyrosine hydroxylase (TH)-positive dopamine neuron loss induced by the administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). MTH1-null mice exhibited a greater accumulation of 8-oxoG in mitochondrial DNA accompanied by a more significant decrease in TH and dopamine transporter immunoreactivities in the striatum after MPTP administration, than in wild-type mice. We thus demonstrated that MTH1 protects the dopamine neurons from oxidative damage in the nucleic acids, especially in the mitochondrial DNA of striatal nerve terminals of dopamine neurons.