MPTP-induced Dopaminergic Cell Loss Research Articles

Neuroprotection by freshwater clam extract against the neurotoxin MPTP in C57BL/6 mice

Freshwater clams are a popular health food in Asia and are traditionally used to prevent hepatic inflammation. Freshwater clam extract (FCE) inhibits inflammatory responses in activated macrophages by reducing the activation of mitogen-activated protein kinase and nuclear factor kappa-light-chain-enhancer of activated B cells. In this study, we used a mouse model of 1-methyl-4-phenyl-1,2,3,6-tetrahydropypridine (MPTP; a neurotoxin)-induced Parkinson’s disease (PD) to demonstrate the protective effect of FCE on dopamine neurons in the substantia nigra pars compacta (SNpc). Locomotor behavior and tyrosine hydroxylase immunohistochemical staining indicated that FCE significantly inhibited MPTP-induced dopaminergic cell loss in the SNpc. Glial fibrillary acidic protein immunohistochemistry and quantitative polymerase chain reaction analysis revealed that astroglial activation and tumor necrosis factor alpha, inducible nitric oxide synthase, and interleukin 1 beta production were significantly inhibited by FCE. The expressions of brain-derived neurotrophic factor, glial cell line-derived neurotrophic factor, and nerve growth factor were markedly increased by FCE action against MPTP-induced toxicity. FCE showed a neuroprotective effect in a MPTP-induced PD model, which might be correlated with anti-inflammation and the stimulation of neurotrophic factors.

Hericium erinaceus mycelium and its isolated erinacine A protection from MPTP-induced neurotoxicity through the ER stress, triggering an apoptosis cascade.

BackgroundHericium erinaceus is an edible mushroom; its various pharmacological effects which have been investigated. This study aimed to demonstrate whether efficacy of oral administration of H. erinaceus mycelium (HEM) and its isolated diterpenoid derivative, erinacine A, can act as an anti-neuroinflammatory agent to bring about neuroprotection using an MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) mouse model of Parkinson’s disease, which results in motor disturbances, in addition to elucidating the mechanisms involved.MethodsMice were treated with and without HEM or erinacine A, after MPTP injection for brain injuries by the degeneration of dopaminergic nigrostriatal neurons. The efficacy of oral administration of HEM improved MPTP-induced loss of tyrosine hydroxylase positive neurons and brain impairment in the substantia nigra pars compacta as measured by brain histological examination.ResultsTreatment with HEM reduced MPTP-induced dopaminergic cell loss, apoptotic cell death induced by oxidative stress, as well as the level of glutathione, nitrotyrosine and 4-hydroxy-2-nonenal (4-HNE). Furthermore, HEM reversed MPTP-associated motor deficits, as revealed by the analysis of rotarod assessment. Our results demonstrated that erinacine A decreases the impairment of MPP-induced neuronal cell cytotoxicity and apoptosis, which were accompanied by ER stress-sustained activation of the IRE1α/TRAF2, JNK1/2 and p38 MAPK pathways, the expression of C/EBP homologous protein (CHOP), IKB-β and NF-κB, as well as Fas and Bax.ConclusionThese physiological and brain histological changes provide HEM neuron-protective insights into the progression of Parkinson’s disease, and this protective effect seems to exist both in vivo and in vitro.

14-3-3 inhibition promotes dopaminergic neuron loss and 14-3-3θ overexpression promotes recovery in the MPTP mouse model of Parkinson’s disease

14-3-3s are a highly conserved protein family that plays important roles in cell survival and interact with several proteins implicated in Parkinson’s disease (PD). Disruption of 14-3-3 expression and function has been implicated in the pathogenesis of PD. We have previously shown that increasing the expression level of 14-3-3θ is protective against rotenone and 1-methyl-4-phenylpyridinium (MPP+) in cultured cells. Here, we extend our studies to examine the effects of 14-3-3s in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD. We first investigated whether targeted nigral 14-3-3θ overexpression mediated by adeno-associated virus offers neuroprotection against MPTP-induced toxicity. 14-3-3θ overexpression using this approach did not reduce MPTP-induced dopaminergic cell loss in the substantia nigra nor the depletion of dopamine (DA) and its metabolites in the striatum at three weeks after MPTP administration. However, 14-3-3θ-overexpressing mice showed a later partial recovery in striatal DA metabolites at eight weeks after MPTP administration compared to controls, suggesting that 14-3-3θ overexpression may help in the functional recovery of those dopaminergic neurons that survive. Conversely, we investigated whether disrupting 14-3-3 function in transgenic mice expressing the pan 14-3-3 inhibitor difopein exacerbates MPTP-induced toxicity. We found that difopein expression promoted dopaminergic cell loss in response to MPTP treatment. Together, these findings suggest that 14-3-3θ overexpression promotes recovery of DA metabolites whereas 14-3-3 inhibition exacerbates neuron loss in the MPTP mouse model of PD.

Phytic acid attenuates inflammatory responses and the levels of NF-κB and p-ERK in MPTP-induced Parkinson’s disease model of mice

Phytic acid (PA) is a naturally occurring constituent which exhibits protective action in Parkinson’s disease (PD). Inflammation in the central nervous system (CNS) is strongly associated with neuronal death in PD. However, the molecular mechanism of the protective effect of PA in PD has not been fully elucidated. In this study, we tried to testify the protection of PA on neuron and inflammatory responses in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD model of mice and investigated the mechanism involved in them. Motor behavior test and tyrosine hydroxylase (TH) immunohistochemistry method showed PA significantly inhibited MPTP-induced dopaminergic cell loss in the substantia nigra (SN). Moreover, using immunohistochemistry method and quantitative polymerase chain reaction (qPCR), microglial activation and inducible nitric oxide synthase (iNOS) were found to be markedly repressed by PA. Via western blot assay, expressions of nuclear factor κB (NF-κB) and phosphorylated extracellular signal-regulated kinase (p-ERK) were significantly attenuated by PA. In conclusion, it is suggested that PA has a neuroprotective effect in MPTP-induced PD model and the neuroprotection is correlated with its anti-inflammatory effect which may be associated with suppression of pathways that involved in NF-κB and p-ERK.

Accumulation of the parkin substrate, FAF1, plays a key role in the dopaminergic neurodegeneration

This study reports the physical and functional interplay between Fas-associated factor 1 (FAF1), a death-promoting protein, and parkin, a key susceptibility protein for Parkinson's disease (PD). We found that parkin acts as an E3 ubiquitin ligase to ubiquitinate FAF1 both in vitro and at cellular level, identifying FAF1 as a direct substrate of parkin. The loss of parkin function due to PD-linked mutations was found to disrupt the ubiquitination and degradation of FAF1, resulting in elevated FAF1 expression in SH-SY5Y cells. Moreover, FAF1-mediated cell death was abolished by wild-type parkin, but not by PD-linked parkin mutants, implying that parkin antagonizes the death potential of FAF1. This led us to investigate whether FAF1 participates in the pathogenesis of PD. To address this, we used a gene trap mutagenesis approach to generate mutant mice with diminished levels of FAF1 (Faf1(gt/gt)). Using the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mouse model of PD, we found that FAF1 accumulated in the substantia nigra pars compacta (SNc) of MPTP-treated PD mice, and that MPTP-induced dopaminergic cell loss in the SNc was significantly attenuated in Faf1(gt/gt) mice versus Faf1(+/+) mice. MPTP-induced reduction of locomotor activity was also lessened in Faf1(gt/gt) mice versus Faf1(+/+) mice. Furthermore, we found that FAF1 deficiency blocked PD-linked biochemical events, including caspase activation, ROS generation, JNK activation and cell death. Taken together, these results suggest a new role for FAF1: that of a positive modulator for PD.

The α7 nAChR Agonist PNU-282987 Reduces Inflammation and MPTP-Induced Nigral Dopaminergic Cell Loss in Mice

Parkinson's disease (PD) is associated with neurodegeneration of dopaminergic neurons and an accompanying neuroinflammatory process in the substantia nigra (SN). The cholinergic anti-inflammatory signalling pathway allows the autonomic nervous system to modulate immunologic stimuli and inflammatory processes. A major component of this pathway is the α7 nicotinic acetylcholine receptor (α7 nACh receptor), which is expressed on immune cells such as microglia. To determine the role of this cholinergic anti-inflammatory signalling pathway, we investigated the effects of the selective α7 nACh agonist PNU-282987 and of the non-competitive nACh antagonist mecamylamine on microglia-induced neuroinflammation and toxin-induced degeneration of dopaminergic neurons in a mouse model of PD. PNU-282987, mecamylamine or placebo administration was started one day before MPTP intoxication and repeated daily until sacrifice after MPTP intoxication. C57Bl/6 mice were injected intraperitoneally four times at 2 h intervals with either 20 mg/kg MPTP-HCl or a corresponding volume of saline. Two or seven days after the end of the MPTP intoxication, the animals were killed and their brains were processed for further analysis. Treatment with PNU-282987 resulted in an attenuation of neuroinflammation in the MPTP-lesioned SN. Furthermore, PNU-282987 attenuated MPTP-induced dopaminergic cell loss in the SN and reduced striatal dopamine depletion. Unexpectedly, mecamylamine lowered neuroinflammation as well, though it did not show a neuroprotective potential at the nigral level. Our results demonstrate the therapeutic potential of the selective α7 nicotinic acetylcholine agonist PNU-282987 in attenuating neuroinflammation and toxin-induced loss of dopaminergic neurons in the acute MPTP mouse model of PD.

Lipid-lowering drugs in the MPTP mouse model of Parkinson's disease: Fenofibrate has a neuroprotective effect, whereas bezafibrate and HMG-CoA reductase inhibitors do not

We tested the ability of simvastatin, atorvastatin, fenofibrate and bezafibrate (two synthetic peroxisome proliferator-activated receptor-alpha (PPAR-alpha) agonists) to prevent dopaminergic cell death in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of Parkinson's disease. Tyrosine hydroxylase (TH) immunochemistry was performed 8 days after acute MPTP intoxication. When orally administered for the week prior to intoxication and a week thereafter, fenofibrate prevented the MPTP-induced dopaminergic cell loss in the substantia nigra pars compacta (SNpc) and attenuated the loss of tyrosine hydroxylase immunoreactivity in the striatum. The dosage of 1-methyl-4-phenyl pyridinium (MPP+) in the striatum by high-performance liquid chromatography indicated that fenofibrate did not affect MPTP metabolism. Bezafibrate had no effect and, strikingly, simvastatin and atorvastatin had a negative effect. We also demonstrated the presence of PPAR-alpha in the dopaminergic neurons of the murine substantia nigra. Our data suggest that PPAR-alpha activation by fenofibrate could have a neuroprotective effect in PD through inhibition of inflammation, oxidative stress and/or apoptosis.

Absence of MPTP-Induced Neuronal Death in Mice Lacking the Dopamine Transporter

MPTP has been shown to induce parkinsonism both in human and in nonhuman primates. The precise mechanism of dopaminergic cell death induced following MPTP treatment is still subject to intense debate. MPP+, which is the oxidation product of MPTP, is actively transported into presynaptic dopaminergic nerve terminals through the plasma membrane dopamine transporter (DAT). In this study, we used mice lacking the DAT by homologous recombination and demonstrated that the MPTP-induced dopaminergic cell loss is dependent on the presence of the DAT. For this we have used tyrosine hydroxylase immunoreactivity (TH-IR) labeling of dopamine cells of the substantia nigra compacta in wild-type, heterozygote, and homozygote mice that were given either saline or MPTP treatments (two ip injections of 30 mg/kg, 10 h apart). Our results show a significant loss of TH-IR in wild type (34.4%), less loss in heterozygotes (22.5%), and no loss in homozygote animals. Thus dopamine cell loss is related to levels of the DAT. These results shed light on the degenerative process of dopamine neurons and suggest that individual differences in developing Parkinson's disease in human may be related to differences of uptake through the DAT of a yet unidentified neurotoxin.

L-Deprenyl and MDL72974 do not improve the recovery of dopaminergic cells following systemic administration of MPTP in mouse

l-Deprenyl, a monoamine oxidase B (MAO-B) inhibitor, administered prior to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) protects dopaminergic neurons against degeneration in several animal species including mice. l-Deprenyl inhibits MPP + formation, the mediator of MPTP toxicity. In addition, l-deprenyl, administered 72 h following MPTP, improves the recovery of tyrosine hydroxylase (TH) immunopositive neurons in the substantia nigra (SN) of mice. This observation lead to the proposal that l-deprenyl exerts a `neurorescue' effect. However, clinical trials failed to demonstrate that l-deprenyl can effectively `rescues' degenerating dopaminergic neurons in early untreated Parkinson's disease (PD) patients. These observations prompted us to reevaluate the long-term impact of l-deprenyl on MPTP-induced dopaminergic cell loss in mice. In addition, we made use of another MAO-B inhibitor, MDL72974, to assess MAO-B participation in this paradigm. Our results suggest that l-deprenyl does not improve the recovery of TH immunopositive neurons in MPTP-treated mice. An apparent reduction in TH + neurons is observed in the SN of MDL72974 and l-deprenyl/MPTP-treated mice at 30 days post-treatment. The possible implication of these findings in relation to the used of MAO-B inhibitors in PD is discussed.

GM-1 ganglioside promotes the recovery of surviving midbrain dopaminergic neurons in MPTP-treated monkeys

We have examined the influence of chronic GM-1 treatment (20mg/kg i.m. for 16 consecutive days) on the extent of dopaminergic damage induced by acute l-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration in cynomolgus monkeys using immunohistochemical and neurochemical analysis. The total number of tyrosine hydroxylase-immunoreactive neurons was reduced in different catecholaminergic mesencephalic regions of MPTP-treated monkeys such as substantia nigra pars compacta, mainly in the ventral portion of the nucleus (39% reduction), substantia nigra pars lateralis (31%), peri- and retrorubral catecholaminergic cell group and ventral tegmental area (A8 and A10 respectively, 20% reduction). A similar degree of neuronal loss was observed in the MPTP + GM-1-treated animals, suggesting that GM-1 ganglioside does not exert a protective effect against MPTP-induced dopaminergic cell loss. Moreover, no neurochemical recovery from the striatal dopaminergic depletion induced by MPTP was found after GM-1 treatment. However, the optical density of tyrosine hydroxylase fibers and the cellular tyrosine hydroxylase content were increased in the substantia nigra pars compacta and ventral tegmental area of the MPTP-treated monkeys which received GM-1 ganglioside, compared with animals treated only with the neurotoxin. These results indicate that GM-1 does not protect against cell death but exerts a neurotrophic effect on surviving dopaminergic neurons in the midbrain of MPTP-lesioned monkeys, suggesting that GM-1 ganglioside may be potentially useful for the treatment of neurodegenerative disorders such as Parkinson's disease.