Cell type-specific gene expression of midbrain dopaminergic neurons reveals molecules involved in their vulnerability and protection

Molecular differences between dopamine (DA) neurons may explain why the mesostriatal DA neurons in the A9 region preferentially degenerate in Parkinson's disease (PD) and toxic models, whereas the adjacent A10 region mesolimbic and mesocortical DA neurons are relatively spared. To characterize innate physiological differences between A9 and A10 DA neurons, we determined gene expression profiles in these neurons in the adult mouse by laser capture microdissection, microarray analysis and real-time PCR. We found 42 genes relatively elevated in A9 DA neurons, whereas 61 genes were elevated in A10 DA neurons [> 2-fold; false discovery rate (FDR) < 1%]. Genes of interest for further functional analysis were selected by criteria of (i) fold differences in gene expression, (ii) real-time PCR validation and (iii) potential roles in neurotoxic or protective biochemical pathways. Three A9-elevated molecules [G-protein coupled inwardly rectifying K channel 2 (GIRK2), adenine nucleotide translocator 2 (ANT-2) and the growth factor IGF-1] and three A10-elevated peptides (GRP, CGRP and PACAP) were further examined in both alpha-synuclein overexpressing PC12 (PC12-alphaSyn) cells and rat primary ventral mesencephalic (VM) cultures exposed to MPP+ neurotoxicity. GIRK2-positive DA neurons were more vulnerable to MPP+ toxicity and overexpression of GIRK2 increased the vulnerability of PC12-alphaSyn cells to the toxin. Blocking of ANT decreased vulnerability to MPP+ in both cell culture systems. Exposing cells to IGF-1, GRP and PACAP decreased vulnerability of both cell types to MPP+, whereas CGRP protected PC12-alphaSyn cells but not primary VM DA neurons. These results indicate that certain differentially expressed molecules in A9 and A10 DA neurons may play key roles in their relative vulnerability to toxins and PD.

Gene transfer of the JNK interacting protein-1 protects dopaminergic neurons in the MPTP model of Parkinson's disease

Increasing evidence suggests that apoptosis may be the underlying cell death mechanism in the selective loss of dopaminergic neurons in Parkinson's disease. Because the inhibition of caspases provides only partial protection in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine/1-methyl-4-phenylpyridinium (MPTP/MPP(+)) model of Parkinson's disease, we investigated the role of the proapoptotic c-Jun N-terminal kinase (JNK) signaling cascade in SH-SY5Y human neuroblastoma cells in vitro and in mice in vivo. MPTP/MPP(+) led to the sequential phosphorylation and activation of JNK kinase (MKK4), JNK, and c-Jun, the activation of caspases, and apoptosis. In mice, adenoviral gene transfer of the JNK binding domain of JNK-interacting protein-1 (a scaffold protein and inhibitor of JNK) inhibited this cascade downstream of MKK4 phosphorylation, blocked JNK, c-Jun, and caspase activation, the death of dopaminergic neurons, and the loss of catecholamines in the striatum. Furthermore, the gene transfer resulted in behavioral benefit. Therefore, inhibition of the JNK pathway offers a new treatment strategy for Parkinson's disease that blocks the death signaling pathway upstream of the execution of apoptosis in dopaminergic neurons, providing a therapeutic advantage over the direct inhibition of caspases.

Genetic ablation of tumor necrosis factor-alpha (TNF-alpha) and pharmacological inhibition of TNF-synthesis attenuates MPTP toxicity in mouse striatum

The impact of pro-inflammatory cytokines such as tumor necrosis factor-alpha (TNF-alpha) in the pathology of Parkinson's disease (PD) and in MPTP neurotoxicity remains unclear. Here, male TNF-alpha (-/-) deficient mice and C57bL/6 mice were treated with MPTP (4 x 15 mg/kg, 24 h intervals) and in one series, thalidomide was administered to inhibit TNF-alpha synthesis. Real-time RT-PCR revealed that the striatal mRNA levels of TNF-alpha, of the astrocytic marker glial fibrillary acidic protein (GFAP) and of the marker for activated microglia, macrophage antigen complex-1 (MAC-1), were significantly enhanced after MPTP administration. Thalidomide (50 mg/kg, p.o.) partly protected against the MPTP-induced dopamine (DA) depletion, and TNF-alpha (-/-) mice showed a significant attenuation of striatal DA and DA metabolite loss as well as striatal tyrosine hydroxylase (TH) fiber density, but no difference in nigral TH and DA transporter immunoreactivity. TNF-alpha deficient mice suffered a lower mortality (10%) compared to the high mortality (75%) seen in wild-type mice after acute MPTP treatment (4 x 20 mg/kg, 2 h interval). HPLC measurement of MPP(+) levels revealed no differences in TNF-alpha (-/-), wild-type and thalidomide treated mice. This study demonstrates that TNF-alpha is involved in MPTP toxicity and that inhibition of TNF-alpha response may be a promising target for extending beyond symptomatic treatment and developing anti-parkinsonian drugs for the treatment of the inflammatory processes in PD.

Cyclooxygenase-2-deficient mice are resistant to 1-methyl-4-phenyl1, 2, 3, 6-tetrahydropyridine-induced damage of dopaminergic neurons in the substantia nigra

Cyclooxygenases (COX), key enzymes in prostanoid biosynthesis, may represent important therapeutic targets in various neurodegenerative diseases. In the present study, we explored the role of COX in Parkinson's disease (PD) by using 1-methyl-4-phenyl1, 2, 3, 6-tetrahydropyridine (MPTP) as a tool to create a rodent Parkinsonian model. MPTP (20 mg/kg, subcutaneously) was injected daily into COX-1- and COX-2-deficient mice and wild-type (WT) controls for five consecutive days. Immunocytochemical analysis of tissues collected 7 days after the final MPTP treatment showed that MPTP significantly decreased the number of tyrosine hydroxylase-immunoreactive (TH-ir) neurons in the substantia nigra pars compacta (SNc) of WT (40% decrease) and COX-1(-/-) (45% decrease) mutants. However, a much smaller loss of TH-ir neurons in COX-2(-/-) mutants (20% decrease) was observed. Furthermore, electrochemical analysis revealed a more than 70% decrease in the levels of dopamine and its metabolites (3,4-dihydroxyphenylacetic acid and homovanillic acid) in the striatum of the WT control COX-1(-/-) and COX-2(-/-) mutant mice. These results indicate that loss of COX-2 activity reduces MPTP-induced damage to the dopaminergic neurons of the SNc, but does not alter the levels of dopamine and its metabolites in the striatum. Interestingly, MPTP caused the same degree of loss of dopaminergic neurons in both COX-2(+/-) and COX-2(-/-) mice (20% loss). The results of this study indicate an important role of COX-2 in MPTP-induced neuronal degeneration and suggest the possibility that manipulation of the COX-2 could be an important target for therapeutic interventions in PD.

Developmental loss and resistance to MPTP toxicity of dopaminergic neurones in substantia nigra pars compacta of gamma-synuclein, alpha-synuclein and double alpha/gamma-synuclein null mutant mice

The growing body of evidence suggests that intermediate products of alpha-synuclein aggregation cause death of sensitive populations of neurones, particularly dopaminergic neurones, which is a critical event in the development of Parkinson's disease and other synucleinopathies. The role of two other members of the family, beta-synuclein and gamma-synuclein, in neurodegeneration is less understood. We studied the effect of inactivation of gamma-synuclein gene on mouse midbrain dopaminergic neurones. Reduced number of dopaminergic neurones was found in substantia nigra pars compacta (SNpc) but not in ventral tegmental area (VTA) of early post-natal and adult gamma-synuclein null mutant mice. Similar reductions were revealed in alpha-synuclein and double alpha-synuclein/gamma-synuclein null mutant animals. However, in none of these mutants did this lead to significant changes of striatal dopamine or dopamine metabolite levels and motor dysfunction. In all three studied types of null mutants, dopaminergic neurones of SNpc were resistant to methyl-phenyl-tetrahydropyridine (MPTP) toxicity. We propose that both synucleins are important for effective survival of SNpc neurones during critical period of development but, in the absence of these proteins, permanent activation of compensatory mechanisms allow many neurones to survive and become resistant to certain toxic insults.

The role of thioredoxin-1 in suppression of endoplasmic reticulum stress in Parkinson disease

Endoplasmic reticulum (ER) stress has been implicated in Parkinson disease. We previously reported that thioredoxin 1 (Trx-1) suppressed the ER stress caused by 1-methy-4-phenyl-1,2,3,6-tetrahydropyridine; however, its molecular mechanism remains largely unknown. In the present study, we showed that 1-methyl-4-phenylpyridinium ion (MPP(+)) induced ER stress by activating glucose-regulated protein 78 (GRP78), inositol-requiring enzyme 1α (IRE1α), tumor necrosis factor receptor-associated factor 2 (TRAF2), c-Jun N-terminal kinase (JNK), caspase-12, and C/EBP homologous protein (CHOP) in PC12 cells. The downregulation of Trx-1 aggravated the ER stress and further increased the expression of the above molecules induced by MPP(+). In contrast, overexpression of Trx-1 attenuated the ER stress and repressed the expression of the above molecules induced by MPP(+). More importantly, the overexpression of Trx-1 in transgenic mice suppressed ER stress by inhibiting the activation of these molecules. We present, for the first time, the molecular mechanism of Trx-1 suppression of endoplasmic reticulum stress in Parkinson disease in vitro and in vivo. Based on our findings, we conclude that Trx-1 plays a neuroprotective role in Parkinson disease by suppressing ER stress by regulating the activation of GRP78, IRE1α, TRAF2, JNK, caspase-12, and CHOP.

Melatonin rescues zebrafish embryos from the parkinsonian phenotype restoring the parkin/PINK1/DJ-1/MUL1 network

Multiple studies reporting mitochondrial impairment in Parkinson's disease (PD) involve knockout or knockdown models to inhibit the expression of mitochondrial-related genes, including parkin, PINK1, and DJ-1 ones. Melatonin has significant neuroprotective properties, which have been related to its ability to boost mitochondrial bioenergetics. The meaning and molecular targets of melatonin in PD are yet unclear. Zebrafish are an outstanding model of PD because they are vertebrates, their dopaminergic system is comparable to the nigrostriatal system of humans, and their brains express the same genes as mammals. The exposure of 24 hpf zebrafish embryos to MPTP leads to a significant inhibition of the mitochondrial complex I and the induction of sncga gene, responsible for enhancing γ-synuclein accumulation, which is related to mitochondrial dysfunction. Moreover, MPTP inhibited the parkin/PINK1/DJ-1 expression, impeding the normal function of the parkin/PINK1/DJ-1/MUL1 network to remove the damaged mitochondria. This situation remains over time, and removing MPTP from the treatment did not stop the neurodegenerative process. On the contrary, mitochondria become worse during the next 2 days without MPTP, and the embryos developed a severe motor impairment that cannot be rescued because the mitochondrial-related gene expression remained inhibited. Melatonin, added together with MPTP or added once MPTP was removed, prevented and recovered, respectively, the parkinsonian phenotype once it was established, restoring gene expression and normal function of the parkin/PINK1/DJ-1/MUL1 loop and also the normal motor activity of the embryos. The results show, for the first time, that melatonin restores brain function in zebrafish suffering with Parkinson-like disease.

Cocaine reward and MPTP toxicity: alteration by regional variant dopamine transporter overexpression

Polygenic factors play important roles in animal models of substance abuse and susceptibility to dopaminergic neurodegeneration. Genetic factors are also likely to contribute to the etiology of human drug abuse disorders, and may alter human vulnerabilities to Parkinsonian neurodegeneration. The dopamine transporter (DAT; SLC6A3) is densely expressed by the dopaminergic midbrain neurons that play central roles in drug reward and is believed to be a primary site of action for cocaine reward. This transporter is necessary for the action of selective dopaminergic neurotoxins, and is uniquely expressed on neurons that are the primary targets of Parkinsonian neurodegeneration. To study possible influences of variant DAT expression on these processes, we have constructed transgenic mice (THDAT) in which tyrosine hydroxylase (TH) promoter sequences drive expression of a rat DAT cDNA variant, increase striatal DAT expression by 20-30%, and provide modest alterations in striatal levels of dopamine and its metabolites. THDAT mice habituate more rapidly to a novel environment than wildtype littermates. These animals display enhanced reward conferred by cocaine, as measured by conditioned place preference. However, locomotor responses to cocaine administration are similar to those of wildtype mice, except at high cocaine doses. THDAT mice display more than 50% greater losses of dopaminergic neurons following a course of MPTP treatment than do wildtype control mice. These results document a model for allelic variation at a gene locus that can exert significant effects in murine models of human substance abuse vulnerability and dopaminergic neurodegeneration.

Role of TNF-alpha receptors in mice intoxicated with the parkinsonian toxin MPTP

The loss of dopaminergic neurons in Parkinson's disease is associated with a glial reaction and the overproduction of proinflammatory cytokines such as tumor necrosis factor alpha (TNF-alpha). TNF-alpha acts via two different receptors, TNFR1 and TNFR2, and is believed to have both a neuroprotective and a deleterious role for neurons. In order to analyze the putative role of TNF-alpha in parkinsonism, we compared the effect of the parkinsonian drug 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in mice lacking TNFR1, TNFR2, or both receptors and in wild-type littermates. We show that MPTP does not affect spontaneous activity or anxiety in any of the groups and that it reduces motor activity on a rotarod in double knock out mice but not in mice lacking only one receptor. Postmortem analysis revealed no differences in the number of nigral dopaminergic neurons whatever the group. In contrast, striatal dopamine level was slightly decreased in double knock-out mice and more reduced by MPTP in this group than in the other groups of mice. In addition, dopamine turnover was significantly more increased in double knock out mice after MPTP injection. These data suggest that TNF-alpha does not participate in the death of dopaminergic neurons in parkinsonism but that it slightly alters dopamine metabolism or the survival of dopaminergic terminals by a mechanism involving both receptors.

Melatonin prevents the dynamin-related protein 1-dependent mitochondrial fission and oxidative insult in the cortical neurons after 1-methyl-4-phenylpyridinium treatment

Mitochondrial dysfunction and oxidative stress are involved in the pathogenesis of Parkinson's disease (PD). Mitochondrial morphology is dynamic and precisely regulated by the mitochondrial fission and fusion machinery. Aberrant mitochondrial fragmentation controlled by the mitochondrial fission protein, dynamin-related protein 1 (Drp1), may result in cell death. Our previous results showed that melatonin protected neurons by inhibiting oxidative stress in a 1-methyl-4-phenylpyridinium (MPP(+) )-induced PD model. However, the effect of melatonin on mitochondrial dynamics remains uncharacterized. Herein, we investigated the effect of melatonin and the role of Drp1 on MPP(+) -induced mitochondrial fission in rat primary cortical neurons. We found that MPP(+) induced a rapid increase in the ratio of GSSG:total glutathione (a marker of oxidative stress) and mitochondrial fragmentation, Drp1 upregulation within 4 hours, and finally resulted in neuron loss 48 hours after the treatment. Neurons overexpressing wild-type Drp1 promoted mitochondrial and nuclear fragmentation; however, neurons overexpressing dominant-negative Drp1(K38A) or cotreated with melatonin exhibited significantly reduced MPP(+) -induced mitochondrial fragmentation and neuron death. Moreover, melatonin cotreatment prevented an MPP(+) -induced high ratio of GSSG and mitochondrial Drp1 upregulation. The prevention of mitochondrial fission by melatonin was not found in neurons transfected with wild-type Drp1. These results provide a new insight that the neuroprotective effect of melatonin against MPP(+) toxicity is mediated by inhibiting the oxidative stress and Drp1-mediated mitochondrial fragmentation.

Reduced MPTP toxicity in noradrenaline transporter knockout mice

The noradrenergic neurons of the locus coeruleus (LC) are damaged in Parkinson's disease (PD). Neurotoxin ablation of the LC noradrenergic neurons has been shown to exacerbate the dopaminergic toxicity of MPTP, suggesting that the noradrenergic system protects dopamine neurons. We utilized mice that exhibit elevated synaptic noradrenaline (NA) by genetically deleting the noradrenaline transporter (NET), a key regulator of the noradrenergic system (NET KO mice). NET KO and wild-type littermates were administered MPTP and striatal dopamine terminal integrity was assessed by HPLC of monoamines, immmunoblotting for dopaminergic markers and tyrosine hydroxylase (TH) immunohistochemistry. MPTP significantly reduced striatal dopamine in wild-type mice, but not in the NET KO mice. To confirm that the protection observed in the NET KO mice was due to the lack of NET, we treated wild-type mice with the specific NET inhibitor, nisoxetine, and then challenged them with MPTP. Nisoxetine conferred protection to the dopaminergic system. These data indicate that NA can modulate MPTP toxicity and suggest that manipulation of the noradrenergic system may have therapeutic value in PD.

DNA damage in brain mitochondria caused by aging and MPTP treatment

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment leads to marked depletion of dopamine (DA) levels in the nigrostriatal pathway and dopaminergic neuronal degeneration in caudate-putamen and substantia nigra. MPTP is believed to inhibit complex I of the electron transport system leading to the generation of reactive oxygen species. We sought to test the hypotheses that MPTP treatment: (1) leads to dopamine depletion; (2) causes extensive mitochondrial DNA damage, and (3) that these effects would be age dependent. The levels of dopamine and its metabolites, DOPAC and HVA were analyzed by HPLC equipped with electrochemical detection. DNA damage was measured by quantitative PCR in both mitochondrial and nuclear (beta-polymerase) targets from the caudate-putamen, substantia nigra and cerebellum regions of control and MPTP-treated mice. The age groups studied were 22 days and 12 months. MPTP produced no significant effect on the levels of dopamine and its metabolites in young mice whereas in old, there was a significant decrease in this neurotransmitter system after MPTP administration. These 12-month-old mice, when compared to the young mice, showed a significant increase in mitochondrial DNA damage in the caudate-putamen and cerebellum. The latter region also displayed a significant increase in DNA damage in a nuclear gene. After treatment with MPTP, there was an age-dependent increase in DNA damage in mitochondria of the caudate-putamen while there was no significant DNA damage in the nuclear target. MPTP treatment led to damage in both mitochondrial and nuclear DNA of the substantia nigra, while there was no damage in either mitochondria or nucleus in cerebellum which was used as a negative control.

Progranulin gene delivery protects dopaminergic neurons in a mouse model of Parkinson's disease

Parkinson’s disease (PD) is a progressive neurodegenerative disorder characterized by tremor, rigidity and akinesia/bradykinesia resulting from the progressive loss of nigrostriatal dopaminergic neurons. To date, only symptomatic treatment is available for PD patients, with no effective means of slowing or stopping the progression of the disease. Progranulin (PGRN) is a 593 amino acid multifunction protein that is widely distributed throughout the CNS, localized primarily in neurons and microglia. PGRN has been demonstrated to be a potent regulator of neuroinflammation and also acts as an autocrine neurotrophic factor, important for long-term neuronal survival. Thus, enhancing PGRN expression may strengthen the cells resistance to disease. In the present study, we have used the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of PD to investigate the possible use of PGRN gene delivery as a therapy for the prevention or treatment of PD. Viral vector delivery of the PGRN gene was an effective means of elevating PGRN expression in nigrostriatal neurons. When PGRN expression was elevated in the SN_C, nigrostriatal neurons were protected from MPTP toxicity in mice, along with a preservation of striatal dopamine content and turnover. Further, protection of nigrostriatal neurons by PGRN gene therapy was accompanied by reductions in markers of MPTP-induced inflammation and apoptosis as well as a complete preservation of locomotor function. We conclude that PGRN gene therapy may have beneficial effects in the treatment of PD.

Neuroinflammation in Parkinson's patients and MPTP-treated mice is not restricted to the nigrostriatal system: microgliosis and differential expression of interleukin-1 receptors in the olfactory bulb

Neuroinflammation may play a role in the pathogenesis of Parkinson's disease (PD). The present study questioned whether this neuroinflammatory response differs between the olfactory bulb, as an early affected region and the nigrostriatal system. Indeed, increased microgliosis was shown in post-mortem olfactory bulb of PD patients. Also in olfactory bulb of MPTP-treated mice, microgliosis and increased expression of IL-1alpha, IL-1beta and IL-1ra mRNA was observed early after treatment. These observations implicate that neuroinflammation is not restricted to the nigrostriatal system. MPTP-induced microgliosis in striatum and olfactory bulb was reduced in IL-1alpha/beta knockout mice, indicating that IL-1 affects microglia activation. Importantly, MPTP induced differential regulation of IL-1 receptors. mRNA levels of IL-1RI and, to a lesser extent, IL-1RII were increased in striatum. Interestingly, in the olfactory bulb only IL-1RII mRNA was enhanced. We suggest that differential regulation of IL-1 signaling can serve as an important mechanism to modulate neuroinflammatory activity after MPTP treatment and possibly during PD.

Pgc-1α overexpression downregulates Pitx3 and increases susceptibility to MPTP toxicity associated with decreased Bdnf

Multiple mechanisms likely contribute to neuronal death in Parkinson's disease (PD), including mitochondrial dysfunction and oxidative stress. Peroxisome proliferator-activated receptor gamma co-activator-1 alpha (PGC-1α) positively regulates the expression of genes required for mitochondrial biogenesis and the cell's antioxidant responses. Also, expression of PGC-1α-regulated genes is low in substantia nigra (SN) neurons in early PD. Thus upregulation of PGC-1α is a candidate neuroprotective strategy in PD. Here, an adeno-associated virus (AAV) was used to induce unilateral overexpression of Pgc-1α, or a control gene, in the SN of wild-type C57BL/6CR mice. Three weeks after AAV administration, mice were treated with saline or MPTP. Overexpression of Pgc-1α in the SN induced expression of target genes, but unexpectedly it also greatly reduced the expression of tyrosine hydroxylase (Th) and other markers of the dopaminergic phenotype with resultant severe loss of striatal dopamine. Reduced Th expression was associated with loss of Pitx3, a transcription factor that is critical for the development and maintenance of dopaminergic cells. Expression of the neurotrophic factor Bdnf, which also is regulated by Pitx3, similarly was reduced. Overexpression of Pgc-1α also led to increased sensitivity to MPTP-induced death of Th+ neurons. Pgc-1α overexpression alone, in the absence of MPTP treatment, did not lead to cell loss in the SN or to loss of dopaminergic terminals. These data demonstrate that overexpression of Pgc-1α results in dopamine depletion associated with lower levels of Pitx3 and enhances susceptibility to MPTP. These data may have ramifications for neuroprotective strategies targeting overexpression of PGC-1α in PD.

The VMAT2 gene in mice and humans: amphetamine responses, locomotion, cardiac arrhythmias, aging, and vulnerability to dopaminergic toxins

Monoamine compartmentalization in monoaminergic neurons uses serial action of the plasma membrane and vesicular monoamine (VAMT2) transporters. We can now define the sequences of the genes encoding these transporters in mice and humans, examine influences of deletions of this gene and alteration in its expression levels in transgenic mice, and identify sequence polymorphisms in the human VMAT2 gene. Examination of VMAT2 variants can provide potential insights into roles for allelic variants at these loci in variant drug responses and in diseases linked to monoaminergic systems, including substance abuse and Parkinson's disease.

miR-103a-3p regulates mitophagy in Parkinson's disease through Parkin/Ambra1 signaling

Parkin is a crucial protein that promotes the clearance of damaged mitochondria via mitophagy in neuron, and parkin mutations result in autosomal-recessive Parkinson's disease (AR-PD). However, the exact mechanisms underlying the regulation of Parkin-mediated mitophagy in PD remain unclear. In this study, PD models were generated through incubation of SH-SY5Y cells with 1-methyl-4-phenylpyridinium ion (MPP⁺, 1.5 mM for 24 h) and intraperitoneal injections of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP, 30 mg/kg for five consecutive days) in mice. A Bioinformatics database was used to identify Parkin-targeting microRNAs (miRNAs). Then, miR-103a-3p agomir, miR-103a-3p antagomir and Parkin siRNA were used to assess the effects of miR-103a-3p/Parkin/Ambra1 signaling-mediated mitophagy in PD in vitro and in vivo. The protein and mRNA levels of Parkin and Ambra1 were significantly decreased, while miR-103a-3p, which is a highly expressed miRNA in the human brain, was obviously increased in PD mouse and SH-SY5Y cell models. Moreover, miR-103a-3p suppressed Parkin expression by targeting a conserved binding site in the 3'-untranslated region (UTR) of Parkin mRNA. Importantly, miR-103a-3p inhibition resulted in neuroprotective effects and improved mitophagy in vitro and in vivo, whereas Parkin siRNA strongly abolished these effects. These findings suggested that miR-103a-3p inhibition has neuroprotective effects in PD, which may be involved in regulating mitophagy through the Parkin/Ambra1 pathway. Modulating miR-103a-3p levels may be an applicable therapeutic strategy for PD.

A disruption mechanism of the molecular clock in a MPTP mouse model of Parkinson's disease

Parkinson's disease (PD) is a common neurodegenerative disorder that is characterized by the degeneration of dopaminergic neurons in the substantia nigra and dopamine depletion in the striatum. Although the motor symptoms are still regarded as the main problem, non-motor symptoms in PD also markedly impair the quality of life. Several non-motor symptoms, such as sleep disturbances and depression, are suggested to be implicated in the alteration in circadian clock function. In this study, we investigated circadian disruption and the mechanism in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD. MPTP-treated mice exhibited altered 24-h rhythms in body temperature and locomotor activity. In addition, MPTP treatment also affected the circadian clock system at the genetic level. The exposure of human neuroblastoma cells (SH-SY5Y) to 1-metyl-4-phenylpyridinium (MPP(+)) increased or decreased the mRNA levels of several clock genes in a dose-dependent manner. MPP(+)-induced changes in clock genes expression were reversed by Compound C, an inhibitor of AMP-activated protein kinase (AMPK). Most importantly, addition of ATP to the drinking water of MPTP-treated mice attenuated neurodegeneration in dopaminergic neurons, suppressed AMPK activation and prevented circadian disruption. The present findings suggest that the activation of AMPK caused circadian dysfunction, and ATP may be a novel therapeutic strategy based on the molecular clock in PD.

Mitochondrial permeability transition pore component cyclophilin D distinguishes nigrostriatal dopaminergic death paradigms in the MPTP mouse model of Parkinson's disease

AIMS

Mitochondrial damage due to Ca(2+) overload-induced opening of permeability transition pores (PTP) is believed to play a role in selective degeneration of nigrostriatal dopaminergic neurons in Parkinson's disease (PD). Genetic ablation of mitochondrial matrix protein cyclophilin D (CYPD) has been shown to increase Ca(2+) threshold of PTP in vitro and to prevent cell death in several in vivo disease models. We investigated the role of CYPD in a mouse model of MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine)-induced PD.

RESULTS

We demonstrate that in vitro, brain mitochondria isolated from CYPD knockout mice were less sensitive to MPP+ (1-methyl-4-phenyl-pyridinium ion)-induced membrane depolarization, and free radical generation compared to wild-type mice. CYPD knockout mitochondria isolated from ventral midbrain of mice treated with MPTP in vivo exhibited less damage as judged from respiratory chain Complex I activity, State 3 respiration rate, and respiratory control index than wild-type mice, whereas assessment of apoptotic markers showed no differences between the two genotypes. However, CYPD knockout mice were significantly resistant only to an acute regimen of MPTP neurotoxicity in contrast to the subacute and chronic MPTP paradigms.

INNOVATION

Inactivation of CYPD is beneficial in preserving mitochondrial functions only in an acute insult model of MPTP-induced dopaminergic neurotoxicity.

CONCLUSION

Our results suggest that CYPD deficiency distinguishes the modes of dopaminergic neurodegeneration in various regimens of MPTP-neurotoxicity.

Overexpression of Parkinson's disease-associated alpha-synucleinA53T by recombinant adeno-associated virus in mice does not increase the vulnerability of dopaminergic neurons to MPTP

Mutations in the alpha-synuclein gene are linked to a rare dominant form of familial Parkinson's disease, and alpha-synuclein is aggregated in Lewy bodies of both sporadic and dominant Parkinson's disease. It has been proposed that mutated alpha-synuclein causes dopaminergic neuron loss by enhancing the vulnerability of these neurons to a variety of insults, including oxidative stress, apoptotic stimuli, and selective dopaminergic neurotoxins, such as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). To test this hypothesis in vivo, we overexpressed human alpha-synuclein(A53T) in the substantia nigra of normal and MPTP-treated mice by rAAV-mediated gene transfer. Determination of dopaminergic neuron survival, striatal tyrosine hydroxylase fiber density, and striatal content of dopamine and its metabolites in rAAV-injected and uninjected hemispheres demonstrated that alpha-synuclein(A53T) does not increase the susceptibility of dopaminergic neurons to MPTP. Our findings argue against a direct detrimental role for (mutant) alpha-synuclein in oxidative stress and/or apoptotic pathways triggered by MPTP, but do not rule out the possibility that alpha-synuclein aggregation in neurons exposed to oxidative stress for long periods of time may be neurotoxic.

Human neural stem cells survive long term in the midbrain of dopamine-depleted monkeys after GDNF overexpression and project neurites toward an appropriate target

Transplanted multipotent human fetal neural stem cells (hfNSCs) significantly improved the function of parkinsonian monkeys in a prior study primarily by neuroprotection, with only 3%-5% of cells expressing a dopamine (DA) phenotype. In this paper, we sought to determine whether further manipulation of the neural microenvironment by overexpression of a developmentally critical molecule, glial cell-derived neurotrophic factor (GDNF), in the host striatum could enhance DA differentiation of hfNSCs injected into the substantia nigra and elicit growth of their axons to the GDNF-expressing target. hfNSCs were transplanted into the midbrain of 10 green monkeys exposed to 1-methyl-4-phenyl-1,2,3,6-tetrahydro-pyridine. GDNF was delivered concomitantly to the striatum via an adeno-associated virus serotype 5 vector, and the fate of grafted cells was assessed after 11 months. Donor cells remained predominantly within the midbrain at the injection site and sprouted numerous neurofilament-immunoreactive fibers that appeared to course rostrally toward the striatum in parallel with tyrosine hydroxylase-immunoreactive fibers from the host substantia nigra but did not mature into DA neurons. This work suggests that hfNSCs can generate neurons that project long fibers in the adult primate brain. However, in the absence of region-specific signals and despite GDNF overexpression, hfNSCs did not differentiate into mature DA neurons in large numbers. It is encouraging, however, that the adult primate brain appeared to retain axonal guidance cues. We believe that transplantation of stem cells, specifically instructed ex vivo to yield DA neurons, could lead to reconstruction of some portion of the nigrostriatal pathway and prove beneficial for the parkinsonian condition.

Ogg1 null mice exhibit age-associated loss of the nigrostriatal pathway and increased sensitivity to MPTP

Cumulative damage to cellular macromolecules via oxidative stress is a hallmark of aging and neurodegenerative disease. Whether such damage is a cause or a subsequent effect of neurodegeneration is still unknown. This paper describes the development of an age-associated mild parkinsonian model in mice that lack the DNA repair enzyme 8-oxoguanine glycosylase 1 (Ogg1). Aged OGG1 knock-out (OGG1 KO) mice show a decreased spontaneous locomotor behavior and evidence a decrease in striatal dopamine levels, a loss of tyrosine hydroxylase (TH)-positive neurons in the substantia nigra (SN), and an increase in ubiquitin-positive inclusions in their remaining SN neurons. In addition, young OGG1 KO mice are more susceptible to the dopaminergic toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) than their wild-type (WT) counterparts. Age-associated increases in 7,8-dihydro-2'-deoxyguanine (oxo(8)dG) have been reported in brain regions and neuronal populations affected in Parkinson's disease (PD), toxin-induced parkinsonian models, and mice harboring genetic abnormalities associated with PD. Because of these increased oxo(8)dG levels, the OGG1 KO mouse strain could shed light on molecular events leading to neuronal loss as a consequence of cumulative oxidative damage to DNA during aging and after toxicological challenge.

DYRK1A promotes dopaminergic neuron survival in the developing brain and in a mouse model of Parkinson's disease

In the brain, programmed cell death (PCD) serves to adjust the numbers of the different types of neurons during development, and its pathological reactivation in the adult leads to neurodegeneration. Dual-specificity tyrosine-(Y)-phosphorylation regulated kinase 1A (DYRK1A) is a pleiotropic kinase involved in neural proliferation and cell death, and its role during brain growth is evolutionarily conserved. Human DYRK1A lies in the Down syndrome critical region on chromosome 21, and heterozygous mutations in the gene cause microcephaly and neurological dysfunction. The mouse model for DYRK1A haploinsufficiency (the Dyrk1a(+/-) mouse) presents neuronal deficits in specific regions of the adult brain, including the substantia nigra (SN), although the mechanisms underlying these pathogenic effects remain unclear. Here we study the effect of DYRK1A copy number variation on dopaminergic cell homeostasis. We show that mesencephalic DA (mDA) neurons are generated in the embryo at normal rates in the Dyrk1a haploinsufficient model and in a model (the mBACtgDyrk1a mouse) that carries three copies of Dyrk1a. We also show that the number of mDA cells diminishes in postnatal Dyrk1a(+/-) mice and increases in mBACtgDyrk1a mice due to an abnormal activity of the mitochondrial caspase9 (Casp9)-dependent apoptotic pathway during the main wave of PCD that affects these neurons. In addition, we show that the cell death induced by 1-methyl-4-phenyl-1,2,3,6 tetrahydropyridine (MPTP), a toxin that activates Casp9-dependent apoptosis in mDA neurons, is attenuated in adult mBACtgDyrk1a mice, leading to an increased survival of SN DA neurons 21 days after MPTP intoxication. Finally, we present data indicating that Dyrk1a phosphorylation of Casp9 at the Thr125 residue is the mechanism by which this kinase hinders both physiological and pathological PCD in mDA neurons. These data provide new insight into the mechanisms that control cell death in brain DA neurons and they show that deregulation of developmental apoptosis may contribute to the phenotype of patients with imbalanced DYRK1A gene dosage.

A DJ-1 Based Peptide Attenuates Dopaminergic Degeneration in Mice Models of Parkinson's Disease via Enhancing Nrf2

Drugs currently used for treating Parkinson's disease patients provide symptomatic relief without altering the neurodegenerative process. Our aim was to examine the possibility of using DJ-1 (PARK7), as a novel therapeutic target for Parkinson's disease. We designed a short peptide, named ND-13. This peptide consists of a 13 amino acids segment of the DJ-1-protein attached to 7 amino acids derived from TAT, a cell penetrating protein. We examined the effects of ND-13 using in vitro and in vivo experimental models of Parkinson's disease. We demonstrated that ND-13 protects cultured cells against oxidative and neurotoxic insults, reduced reactive oxygen species accumulation, activated the protective erythroid-2 related factor 2 system and increased cell survival. ND-13 robustly attenuated dopaminergic system dysfunction and in improved the behavioral outcome in the 6-hydroxydopamine mouse model of Parkinson's disease, both in wild type and in DJ-1 knockout mice. Moreover, ND-13 restored dopamine content in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine mouse model. These findings validate DJ-1 as a promising therapeutic target in Parkinson's disease and identify a novel peptide with clinical potential, which may be significant for a broader range of neurological diseases, possibly with an important impact for the neurosciences.

Targeted Overexpression of α-Synuclein by rAAV2/1 Vectors Induces Progressive Nigrostriatal Degeneration and Increases Vulnerability to MPTP in Mouse

Mutations, duplication and triplication of α-synuclein genes are linked to familial Parkinson's disease (PD), and aggregation of α-synuclein (α-syn) in Lewy bodies (LB) is involved in the pathogenesis of the disease. The targeted overexpression of α-syn in the substantia nigra (SN) mediated by viral vectors may provide a better alternative to recapitulate the neurodegenerative features of PD. Therefore, we overexpressed human wild-type α-syn using rAAV2/1 vectors in the bilateral SN of mouse and examined the effects for up to 12 weeks. Delivery of rAAV-2/1-α-syn caused significant nigrostriatal degeneration including appearance of dystrophic striatal neurites, loss of nigral dopaminergic (DA) neurons and dissolving nigral neuron bodies in a time-dependent manner. In addition, the α-syn overexpressed mice also developed significant deficits in motor function at 12 weeks when the loss of DA neurons exceeded a threshold of 50%. To investigate the sensitivity to neurotoxins in mice overexpressing α-syn, we performed an MPTP treatment with the subacute regimen 8 weeks after rAAV injection. The impact of the combined genetic and environmental insults on DA neuronal loss, striatal dopamine depletion, dopamine turnover and motor dysfunction was markedly greater than that of either alone. Moreover, we observed increased phosphorylation (S129), accumulation and nuclear distribution of α-syn after the combined insults. In summary, these results reveal that the overexpressed α-syn induces progressive nigrostriatal degeneration and increases the susceptibility of DA neurons to MPTP. Therefore, the targeted overexpression of α-syn and the combination with environmental toxins may provide valuable models for understanding PD pathogenesis and developing related therapies.