Proteasome Inhibitors Protect Against Degeneration of Nigral Dopaminergic Neurons in Hemiparkinsonian Rats

Therapeutic Implications and Regulations of Protein Post-translational Modifications in Parkinsons Disease

Parkinsons disease (PD) is a neurodegenerative disorder characterized by dopaminergic neuron loss and alpha-synuclein aggregation. This comprehensive review examines the intricate role of post-translational modifications (PTMs) in PD pathogenesis, focusing on DNA methylation, histone modifications, phosphorylation, SUMOylation, and ubiquitination. Targeted PTM modulation, particularly in key proteins like Parkin, DJ1, and PINK1, emerges as a promising therapeutic strategy for mitigating dopaminergic degeneration in PD. Dysregulated PTMs significantly contribute to the accumulation of toxic protein aggregates and dopaminergic neuronal dysfunction observed in PD. Targeting PTMs, including epigenetic strategies, addressing aberrant phosphorylation events, and modulating SUMOylation processes, provides potential avenues for intervention. The ubiquitin-proteasome system, governed by enzymes like Parkin and Nedd4, offers potential targets for clearing misfolded proteins and developing disease-modifying interventions. Compounds like ginkgolic acid, SUMO E1 enzyme inhibitors, and natural compounds like Indole-3-carbinol illustrate the feasibility of modulating PTMs for therapeutic purposes in PD. This review underscores the therapeutic potential of PTM-targeted interventions in modulating PD-related pathways, emphasizing the need for further research in this promising area of Parkinsons disease therapeutics.

Lack of Parkinsonian Pathology and Neurodegeneration in Mice After Long-Term Injections of a Proteasome Inhibitor in Olfactory Bulb and Amygdala

Proteinaceous inclusions, called Lewy bodies (LBs), are used as a pathological hallmark for Parkinson's disease (PD). Recent studies suggested a prion-like spreading mechanism for α-synucleinopathy where early neuropathological deposits occur, among others, in the olfactory bulb (OB) and amygdala. LBs contain insoluble α-synuclein and many other ubiquitinated proteins, suggesting a role of protein degradation system failure in PD pathogenesis. Therefore, we wanted to study the effects of a proteasomal inhibitor, lactacystin, on the aggregability and transmissibility of α-synuclein in the OB and amygdala. We performed injections of lactacystin in the OB and amygdala of wild-type mice. Motor behavior, markers of neuroinflammation, α-synuclein, and dopaminergic integrity were assessed by immunohistochemistry. Overall, there were no differences in the number of neurons and α-synuclein expression in these regions following injection of lactacystin into either the OB or amygdala. Microglial and astroglial labeling appeared to be correlated with surgery-induced inflammation or local effects of lactacystin. Consistent with the behavior and pathological findings, there was no loss of dopaminergic cell bodies in the substantia nigra and terminals in the striatum. Our data showed that long-term lactacystin injections in extra nigrostriatal regions may not mimic spreading aspects of PD and reinforce the special vulnerability of dopaminergic neurons of the substantia nigra pars compacta (SNc).

Regulation of aberrant proteasome activity re-establishes plasticity and long-term memory in an animal model of Alzheimer's disease

Reduced retrograde memory performance at the cognitive level and aggregation/deposition of amyloid beta (Aβ) in the brain at the cellular level are some of the hallmarks of Alzheimer's Disease (AD). A molecular system that participates in the removal of proteins with an altered conformation is the Ubiquitin-Proteasome System (UPS). Impairments of the UPS in wild-type (WT) mice lead to defective clearance of Aβ and prevent long-term plasticity of synaptic transmission. Here we show data whereby in contrast to WT mice, the inhibition of proteasome-mediated protein degradation in an animal model of AD by MG132 or lactacystin restores impaired activity-dependent synaptic plasticity and its associative interaction, synaptic tagging and capture (STC) in vitro, as well as associative long-term memory in vivo. This augmentation of synaptic plasticity and memory is mediated by the mTOR pathway and protein synthesis. Our data offer novel insights into the rebalancing of proteins relevant for synaptic plasticity which are regulated by UPS in AD-like animal models. In addition, the data provide evidence that proteasome inhibitors might be effective in reinstating synaptic plasticity and memory performance in AD, and therefore offer a new potential therapeutic option for AD treatment.

Methionine sulfoxide reductase (Msr) dysfunction in human brain disease

Extensive research has shown that oxidative stress is strongly associated with aging, senescence and several diseases, including neurodegenerative and psychiatric disorders. Oxidative stress is caused by the overproduction of reactive oxygen species (ROS) that can be counteracted by both enzymatic and nonenzymatic antioxidants. One of these antioxidant mechanisms is the widely studied methionine sulfoxide reductase system (Msr). Methionine is one of the most easily oxidized amino acids and Msr can reverse this oxidation and restore protein function, with MsrA and MsrB reducing different stereoisomers. This article focuses on experimental and genetic research performed on Msr and its link to brain diseases. Studies on several model systems as well as genome-wide association studies are compiled to highlight the role of MSRA in schizophrenia, Alzheimer's disease, and Parkinson's disease. Genetic variation of MSRA may also contribute to the risk of psychosis, personality traits, and metabolic factors.

Proteasome inhibition by MG-132 protects against deltamethrin-induced apoptosis in rat hippocampus

AIMS

Deltamethrin (DM), a type II synthetic pyrethroid insecticide, is widely used in agriculture and home pest control. The evaluation of their toxic effects is of major concern to public health. However, the molecular mechanism of DM-induced neurodegenerative disease is still far from clear. This study was designed to investigate the potential role of ubiquitin proteasome system (UPS) in DM-induced neurotoxicity where the proteasome inhibitor MG-132 could mitigate the neurotoxic effects.

MAIN METHODS

Male Sprague-Dawley rats were divided into two batches. The first batch of rats was administrated with a single dose of DM (12.5 mg/kg) by intraperitoneal injections (i.p.) and the animals were then euthanized at 5, 24, and 48 h post injection. The second batch was treated as follow: control group, DM (12.5 mg/kg) groups for 24 h, MG-132 (0.5 mg/kg, i.p.) 2 h plus DM 24 h group, and MG-132 alone group. Ubiqutinatied proteins, DNA damage and apoptosis were investigated.

KEY FINDINGS

DM treatment induced the ubiquitinated proteins expression with the peaks at 5 h. Moreover, DM increased DNA damage, early apoptotic rate, the expression level of Cleaved Caspase-3, caspase-3 activity and decreased the expression level of Bcl-2 at DM 24 h group. Compared to DM 24 h group, MG-132 pretreatment significantly down-regulated ubiquitinated proteins, lowered the DNA damage and apoptosis by decreasing Caspase-3 and increasing Bcl-2 expression.

SIGNIFICANCE

These results indicate that MG-132 effectively alleviates DM-induced DNA damage and apoptosis by inhibiting ubiquitinated proteins. UPS may play a role in DM-induced neurodegenerative disorders.

Longitudinal monoaminergic PET imaging of chronic proteasome inhibition in minipigs

Impairment of the ubiquitin proteasome system has been implicated in Parkinson’s disease. We used positron emission tomography to investigate longitudinal effects of chronic intracerebroventricular exposure to the proteasome inhibitor lactacystin on monoaminergic projections and neuroinflammation. Göttingen minipigs were implanted in the cisterna magna with a catheter connected to a subcutaneous injection port. Minipigs were imaged at baseline and after cumulative doses of 200 and 400 μg lactacystin, respectively. Main radioligands included [¹¹C]-DTBZ (vesicular monoamine transporter type 2) and [¹¹C]-yohimbine (α2-adrenoceptor). [¹¹C]-DASB (serotonin transporter) and [¹¹C]-PK11195 (activated microglia) became available later in the study and we present their results in a smaller subset of animals for information purposes only. Striatal [¹¹C]-DTBZ binding potentials decreased significantly by 16% after 200 μg compared to baseline, but the decrease was not sustained after 400 μg (n = 6). [¹¹C]-yohimbine volume of distribution increased by 18–25% in the pons, grey matter and the thalamus after 200 μg, which persisted at 400 μg (n = 6). In the later subset of minipigs, we observed decreased [¹¹C]-DASB (n = 5) and increased [¹¹C]-PK11195 (n = 3) uptake after 200 μg. These changes may mimic monoaminergic changes and compensatory responses in early Parkinson’s disease.

Removal of prolyl oligopeptidase reduces alpha-synuclein toxicity in cells and in vivo

Prolyl oligopeptidase (PREP) inhibition by small-molecule inhibitors can reduce alpha-synuclein (aSyn) aggregation, a key player in Parkinson's disease pathology. However, the significance of PREP protein for aSyn aggregation and toxicity is not known. We studied this in vivo by using PREP knock-out mice with viral vector injections of aSyn and PREP. Animal behavior was studied by locomotor activity and cylinder tests, microdialysis and HPLC were used to analyze dopamine levels, and different aSyn forms and loss of dopaminergic neurons were studied by immunostainings. Additionally, PREP knock-out cells were used to characterize the impact of PREP and aSyn on autophagy, proteasomal system and aSyn secretion. PREP knock-out animals were nonresponsive to aSyn-induced unilateral toxicity but combination of PREP and aSyn injections increased aSyn toxicity. Phosphorylated p129, proteinase K resistant aSyn levels and tyrosine hydroxylase positive cells were decreased in aSyn and PREP injected knock-out animals. These changes were accompanied by altered dopamine metabolite levels. PREP knock-out cells showed reduced response to aSyn, while cells were restored to wild-type cell levels after PREP overexpression. Taken together, our data suggests that PREP can enhance aSyn toxicity in vivo.

The Proteasome Inhibition Model of Parkinson's Disease

The pathological hallmarks of Parkinson's disease are the progressive loss of nigral dopaminergic neurons and the formation of intracellular inclusion bodies, termed Lewy bodies, in surviving neurons. Accumulation of proteins in large insoluble cytoplasmic aggregates has been proposed to result, partly, from a failure in the function of intracellular protein degradation pathways. Evidence in support for such a hypothesis emerged in the beginning of the years 2000 with studies demonstrating structural and functional deficits in the ubiquitin-proteasome pathway in post-mortem nigral tissue of patients with Parkinson's disease. These fundamental findings have inspired the development of a new generation of animal models based on the use of proteasome inhibitors to disturb protein homeostasis and trigger nigral dopaminergic neurodegeneration. In this review, we provide an updated overview of the current approaches in employing proteasome inhibitors to model Parkinson's disease, with particular emphasis on rodent studies. In addition, the mechanisms underlying proteasome inhibition-induced cell death and the validity criteria (construct, face and predictive validity) of the model will be critically discussed. Due to its distinct, but highly relevant mechanism of inducing neuronal death, the proteasome inhibition model represents a useful addition to the repertoire of toxin-based models of Parkinson's disease that might provide novel clues to unravel the complex pathogenesis of this disorder.

Nigral proteasome inhibition in mice leads to motor and non-motor deficits and increased expression of Ser129 phosphorylated α-synuclein

Parkinson's disease is a neurodegenerative disorder characterized by motor and non-motor disturbances. Various pathogenic pathways drive disease progression including oxidative stress, mitochondrial dysfunction, α-synuclein aggregation and impairment of protein degradation systems. Dysfunction of the ubiquitin-proteasome system in the substantia nigra of Parkinson's disease patients is believed to be one of the causes of protein aggregation and cell death associated with this disorder. Lactacystin, a potent inhibitor of the proteasome, was previously delivered to the nigrostriatal pathway of rodents to model nigrostriatal degeneration. Although lactacystin-treated animals develop parkinsonian motor impairment, it is currently unknown whether they also develop non-motor symptoms characteristic of this disorder. In order to further describe the proteasome inhibition model of Parkinson's disease, we characterized the unilateral lactacystin model, performed by stereotaxic injection of the toxin in the substantia nigra of mice. We studied the degree of neurodegeneration and the behavioral phenotype 1 and 3 weeks after lactacystin lesion both in terms of motor impairment, as well as non-motor symptoms. We report that unilateral administration of 3 μg lactacystin to the substantia nigra of mice leads to partial (~40%) dopaminergic cell loss and concurrent striatal dopamine depletion, accompanied by increased expression of Ser129-phosphorylated α-synuclein. Behavioral characterization of the model revealed parkinsonian motor impairment, as well as signs of non-motor disturbances resembling early stage Parkinson's disease including sensitive and somatosensory deficits, anxiety-like behavior, and perseverative behavior. The consistent finding of good face validity, together with relevant construct validity, warrant a further evaluation of proteasome inhibition models of Parkinson's disease in pre-clinical research and validation of therapeutic targets.

Lack of neuroprotective effect of celastrol under conditions of proteasome inhibition by lactacystin in in vitro and in vivo studies: implications for Parkinson's disease

A number of studies suggest that the ubiquitin-proteasome system (UPS) impairment may underlie neuronal death in Parkinson's disease. Celastrol is a neuroprotective agent with anti-inflammatory and antioxidant properties. The aim of this study was to determine whether celastrol may exert neuroprotective effects both in vitro and in vivo under conditions of the lactacystin-induced UPS inhibition. In the in vitro study, mouse primary cortical neurons and neuroblastoma SH-SY5Y cells were incubated with lactacystin for 48 h (2.5 and 10 μg/ml, respectively). The animal study was performed on male Wistar rats injected unilaterally with lactacystin (5 μg/2 μl) into the substantia nigra (SN) pars compacta. In the in vitro study, we did not found any protective effects of celastrol, given either in the pre- or co-treatment mode. Moreover, in the higher concentrations, celastrol itself reduced cell viability, and enhanced the lactacystin-induced cell death in both types of cells. In the in vivo study, none of the celastrol doses (0.3-3 mg/kg) attenuated the lactacystin-induced decrease in the level of dopamine (DA) and its metabolites or protected nigral dopaminergic neurons against the lactacystin-induced degeneration. The highest celastrol dose potentiated the lactacystin-induced decrease in the level of DA and its metabolites in the lesioned striatum, and accelerated the lactacystin-induced increase in the oxidative and total metabolism of DA. Moreover, when given alone, this dose of celastrol bilaterally decreased the number and/or density of dopaminergic neurons in the SN. Our results demonstrate that celastrol does not induce neuroprotective effects under conditions of UPS inhibition.

Ubiquitin-proteasome system impairment and MPTP-induced oxidative stress in the brain of C57BL/6 wild-type and GSTP knockout mice

The ubiquitin-proteasome system (UPS) is the primary proteolytic complex responsible for the elimination of damaged and misfolded intracellular proteins, often formed upon oxidative stress. Parkinson's disease (PD) is neuropathologically characterized by selective death of dopaminergic neurons in the substantia nigra (SN) and accumulation of intracytoplasmic inclusions of aggregated proteins. Along with mitochondrial dysfunction and oxidative stress, defects in the UPS have been implicated in PD. Glutathione S-transferase pi (GSTP) is a phase II detoxifying enzyme displaying important defensive roles against the accumulation of reactive metabolites that potentiate the aggression of SN neuronal cells, by regulating several processes including S-glutathionylation, modulation of glutathione levels and control of kinase-catalytic activities. In this work we used C57BL/6 wild-type and GSTP knockout mice to elucidate the effect of both MPTP and MG132 in the UPS function and to clarify if the absence of GSTP alters the response of this pathway to the neurotoxin and proteasome inhibitor insults. Our results demonstrate that different components of the UPS have different susceptibilities to oxidative stress. Importantly, when compared to the wild-type, GSTP knockout mice display decreased ubiquitination capacity and overall increased susceptibility to UPS damage and inactivation upon MPTP-induced oxidative stress.

Neuroprotective effects of longan ( Dimocarpus longan Lour.) flower water extract on MPP+-induced neurotoxicity in rat brain

In this study, the neuroprotective effect of Dimocarpus longan Lour. flower water extract (LFWE) was investigated. First, an in vitro study showed that LFWE concentration-dependently inhibited lipid peroxidation of brain homogenates incubated at 37 °C. The antioxidative activity of LFWE was more potent than that of glutathione or Trolox. Furthermore, an ex vivo study found that the basal lipid peroxidation (0 °C) and lipid peroxidation incubated at 37 °C were lower in the brain homogenates of LFWE-treated (500 mg/day) rats, indicating that the brain of LFWE-treated rats was more resistant to oxidative stress. Moreover, a Parkinsonian animal model was employed to demonstrate that oral administration of LFWE (125-500 mg/kg/day) dose-dependently attenuated 1-methyl-4-phenylpyridinium (MPP(+))-induced neurotoxicity in the nigrostriatal dopaminergic system of rat brain. In conclusion, this study suggests that LFWE is antioxidative, anti-inflammatory, and anti-apoptotic. Furthermore, oral administration of LFWE appears to be useful in preventing and/or treating central nervous system neurodegenerative diseases, including Parkinsonism.

Inducers and co-inducers of molecular chaperones

Molecular chaperones, which are mostly heat- or stress-induced proteins (HSPs), not only regulate various cellular functions such as protein folding, refolding of partially denatured proteins, protein transport across membranes, cytoskeletal organization, degradation of disabled proteins, and apoptosis, but also act as cytoprotective factors against deleterious environmental stresses. Recent studies indicated that moderate overexpression of molecular chaperones could confer cells and tissues stress tolerance and provide beneficial effects on various pathological states associated with protein misfolding and protein aggregation. Mild heat shock, transfection of HSP genes, and some chemical compounds are the major means of overexpression of molecular chaperones. In this review, we summarize recent studies of chemical compounds that could induce or enhance the expression of molecular chaperones or HSPs.

Effects of proteasome inhibitors on rat renal fibrosis in vitro and in vivo

AIM

Transforming growth factor-β (TGF-β) is involved in renal tubulointerstitial fibrosis. Recently, the ubiquitin proteasome system was shown to participate in the TGF-β signalling pathway. The aim of this study was to examine the effects of proteasome inhibitors on TGF-β-induced transformation of renal fibroblasts and tubular epithelial cells in vitro and on unilateral ureteral obstruction (UUO) in vivo.

METHODS

Rat renal fibroblasts NRK-49F cells and tubular epithelial cells, NRK-52E, were treated with TGF-β in the presence or absence of a proteasome inhibitor, MG132 or lactacystin. Rats were subjected to UUO and received MG132 i.p. for 7 days.

RESULTS

In cultured renal cells, both MG132 and lactacystin inhibited TGF-β-induced α-smooth muscle actin (α-SMA) protein expression according to both western blotting and immunofluorescent study results. MG132 also suppressed TGF-β-induced mRNA expression of α-SMA and upregulation of Smad-response element reporter activity. However, MG132 did not inhibit TGF-β-induced phosphorylation and nuclear translocation of Smad2. In contrast, MG132 increased the protein level of Smad co-repressor SnoN, demonstrating that SnoN is one of the target molecules by which MG132 blocks the TGF-β signalling pathway. Although the proteasome inhibitor suppressed TGF-β-induced transformation of cultured fibroblasts and tubular epithelial cells, MG132 treatment did not ameliorate tubulointerstitial fibrosis in the rat UUO model.

CONCLUSION

Proteasome inhibitors attenuate TGF-β signalling by blocking Smad signal transduction in vitro, but do not inhibit renal interstitial fibrosis in vivo.

Selective susceptibility of human dopaminergic neural stem cells to dopamine-induced apoptosis

Dysfunctions of ubiquitin-proteasome system and toxicity of dopamine have been known as the key mechanisms in the pathogenesis of Parkinson's disease (PD) and proteasome inhibitors are widely used in experimental models of PD to reproduce cell death of dopaminergic neurons. In the present study, immortalized human neural stem cells (HB1.F3, F3) and those transfected with human aromatic acid decarboxylase gene (F3.AADC), were used to investigate the mechanism of selective dopaminergic neuronal cell death mediated by dopamine or proteasome inhibitors. Flow cytometric analysis revealed that F3.AADC was more susceptible to dopamine than parental F3 cell which does not carry dopaminergic phenotype. The dopamine-induced apoptosis was mediated by activation of caspases 3 and 9 and cleavage of PARP. Proteasome inhibitors also induced apoptosis in dose-dependent manner but there was no difference between cell types. Prolonged exposure to subtoxic dose of proteasome inhibitors further enhanced dopamine-induced apoptosis in the F3.AADC, and increased presence of alpha-synuclein and ubiquitin-positive inclusions was noted in the cytoplasm of apoptotic cells by immunocytochemistry. These findings indicate that dopaminergic cells are selectively susceptible to dopamine toxicity and prolonged suppression of proteasome system further enhances selective sensitivity to dopamine toxicity. Chronic subtoxic proteasomal dysfunction of dopaminergic cells might contribute to selective cell death of dopaminergic neurons during the pathogenesis of Parkinson's disease.

[Dopaminergic neuroprotection and reconstruction of neural network tiara]

Parkinson's disease (PD) is an age-related neurodegenerative disorder in whose brain massive loss of dopaminergic neurons and formation of Lewy bodies occur in the substantia nigra (SN). L-Dihydroxyphenylamine (L-DOPA) substitution is still considered the gold standard of antiparkinsonian drug therapy. However, there has been little information available on neuroprotective and regenerative therapies. Recently, we have found that pramipexole and talipexole (D(2)/D(3)-dopaminergic agonists) inhibit dopaminergic neurotoxin-induced production of reactive oxygen species and apoptotic cell death. In addition, treatment with these drugs induces enhancement of anti-apoptotic Bcl-2 expression and inhibition of α-synuclein aggregation. Interestingly, recent study suggests that pramipexole treatment delays the progression of early PD symptom. On the other hand, we investigated the transplantation strategy for PD by assessing whether double-transplants of mouse embryonic stem (ES) cell-derived neurons in the striatum (ST) and SN, or subthalamic nucleus (STN), induce functional recovery in rat hemi-parkinsonian model. The study indicates that both the involvement of ST as a place of transplantation and the number of ES cell-derived neurons are essential factors for efficacy on PD animal model. Interestingly, an invertebrate planarian can regenerate complete organs, including a well-organized central nervous system (brain), within about 7 days. The regeneration process of the planarian dopaminergic neural network (tiara) may be divided into five steps: 1) anterior blastema formation, 2) brain rudiment formation, 3) brain pattern formation, 4) the formation of dopaminergic tiara, and 5) functional recovery of dopaminergic motor regulation, with several kinds of genes and molecular cascades acting at each step.

Elevation of heme oxygenase-1 by proteasome inhibition affords dopaminergic neuroprotection

Postmortem studies have shown that heme oxygenase-1 (HO-1) immunoreactivity is increased in patients with Parkinson disease. HO-1 expression is highly upregulated by a variety of stress. Since the proteasome activity is decreased in patients with Parkinson disease, we investigated whether proteasome activity regulates HO-1 content. MG-132, a proteasome inhibitor, increased the amount of HO-1 protein mainly in astrocytes of primary mesencephalic cultures. Quantitative RT-PCR analysis revealed that lactacystin upregulated HO-1 mRNA expression. Proteasome inhibition with MG132 also increased the cytomegalovirus promoter-driven expression of Flag-HO-1 protein and resulted in an accumulation of ubiquitinated Flag-HO-1 in Flag-HO-1-overexpressing PC12 cells. In addition, a cycloheximide chase assay demonstrated that the degradation of Flag-HO-1 protein was slowed by MG-132. Next, the function of HO-1 which was upregulated by proteasome inhibitors was examined. Proteasome inhibitors protected dopaminergic neurons from 6-hydroxydopamine (6-OHDA)-induced toxicity and this neuroprotection was abrogated by co-treatment with zinc protoporphyrin IX, a HO-1 inhibitor. Furthermore, 6-OHDA-induced toxicity was blocked by bilirubin and carbon monoxide, products of the HO-1-catalyzed degradation of heme. These results suggest that mesencephalic HO-1 protein level is regulated by proteasome activity and the elevation by proteasome inhibition affords neuroprotection.

Oxidative-stress-induced alterations in Sp factors mediate transcriptional regulation of the NR1 subunit in hippocampus during hypoxia

Ascent to high altitude is associated with tissue hypoxia resulting from the decrease in partial pressure of atmospheric oxygen. The hippocampus, in particular, is highly vulnerable to hypoxic insult, which at least in part can be attributed to the occurrence of glutamate excitotoxicity. Although this excitotoxic damage is often related to increased NMDA receptor activation and subsequent calcium-mediated free radical generation, the mechanisms involving the transcriptional regulation of NMDA receptor subunit expression by hypoxic stress remains to be explored. Our study reveals a novel mechanism for the regulation of expression of the NR1 subunit of NMDA receptors by the Sp family of transcription factors through an oxidative-stress-mediated mechanism that also involves the molecular chaperone Hsp90. The findings not only show the occurrence of lipid peroxidation and DNA damage in hippocampal cells exposed to hypoxia but also reveal a calcium-independent mechanism of selective oxidation and degradation of Sp3 by the 20S proteasome. This along with increased DNA binding activity of Sp1 leads to NR1 upregulation in the hippocampus during hypoxic stress. The study therefore provides evidence for free radical-mediated regulation of gene expression in hypoxia and the scope of the use of antioxidants in preventing excitotoxic neuronal damage during hypoxia.

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.

Adaptation to chronic MG132 reduces oxidative toxicity by a CuZnSOD-dependent mechanism

To study whether and how cells adapt to chronic cellular stress, we exposed PC12 cells to the proteasome inhibitor MG132 (0.1 microM) for 2 weeks and longer. This treatment reduced chymotrypsin-like proteasome activity by 47% and was associated with protection against both 6-hydroxydopamine (6-OHDA; 100 microM) and higher dose MG132 (40 microM). Protection developed slowly over the course of the first 2 weeks of exposure and was chronic thereafter. There was no change in total GSH levels after MG132. Buthionine sulfoximine (100 microM) reduced GSH levels by 60%, but exacerbated 6-OHDA toxicity to the same extent in both MG132-treated and control cells and failed to reduce MG132-induced protection. Chronic MG132 resulted in elevated antioxidant proteins CuZn superoxide dismutase (SOD; +55%), MnSOD (+21%), and catalase (+15%), as well as chaperone heat-shock protein 70 (+42%). Examination of SOD enzyme activity revealed higher levels of CuZnSOD (+40%), with no change in MnSOD. We further assessed the mechanism of protection by reducing CuZnSOD levels with two independent siRNA sequences, both of which successfully attenuated protection against 6-OHDA. Previous reports suggested that artificial over-expression of CuZnSOD in dopaminergic cells is protective. Our data complement such observations, revealing that dopaminergic cells are also able to use endogenous CuZnSOD in self-defensive adaptations to chronic stress, and that they can even do so in the face of extensive GSH loss.

Neurodegeneration and motor dysfunction in a conditional model of Parkinson's disease

Alpha-synuclein (alpha-syn) has been implicated in the pathogenesis of many neurodegenerative disorders, including Parkinson's disease. These disorders are characterized by various neurological and psychiatric symptoms based on progressive neuropathological alterations. Whether the neurodegenerative process might be halted or even reversed is presently unknown. Therefore, conditional mouse models are powerful tools to analyze the relationship between transgene expression and progression of the disease. To explore whether alpha-syn solely originates and further incites these alterations, we generated conditional mouse models by using the tet-regulatable system. Mice expressing high levels of human wild-type alpha-syn in midbrain and forebrain regions developed nigral and hippocampal neuropathology, including reduced neurogenesis and neurodegeneration in absence of fibrillary inclusions, leading to cognitive impairment and progressive motor decline. Turning off transgene expression in symptomatic mice halted progression but did not reverse the symptoms. Thus, our data suggest that approaches targeting alpha-syn-induced pathological pathways might be of benefit rather in early disease stages. Furthermore, alpha-syn-associated cytotoxicity is independent of filamentous inclusion body formation in our conditional mouse model.

Proteasomal inhibition and apoptosis regulatory changes in human isolated lymphocytes: The synergistic role of dopamine

Abnormal deposition of protein aggregates and increased susceptibility to apoptotic cell death may result from defects in the activity of the ubiquitin-proteasome system (UPS); neurotoxicity related to UPS defects seems to require dopamine to be fully expressed. The aim of this study was to investigate the pro-apoptotic effects caused by proteasomal activity inhibition, as well as the synergistic effect of dopaminergic stimulation in human lymphocytes isolated from healthy volunteers. Cells were incubated 20 h at 37 degrees C, with: (1) lactacystin, (2) increasing concentrations of dopamine or (3) mixture of dopamine and lactacystin. Activities of proteasome 20S and pro-apoptotic caspases-3 and -9 and levels of anti-apoptotic Bcl-2 were measured with fluorimetric or immunochemical assays, while a "DNA diffusion" assay was used to determine the apoptosis. Incubation of lymphocytes with lactacystin, which caused reduction of proteasomal activity, was associated with activation of caspases. A clear, dose-dependent reduction of proteasomal activity was also seen in the presence of increasing doses of dopamine, which was accompanied by a slight dose-dependent increase of caspases activities and Bcl-2 levels. Both effects on proteasome and caspase activities were enhanced when cells were simultaneously exposed to lactacystin and elevated concentrations of dopamine. Apoptosis was detected in all treated samples, but not in controls, without significant differences among the treatment groups; however, the association of dopamine and lactacystin induced a clear reduction in the number of cells being analyzed, pointing to marked cytotoxicity. Our data confirm the potentiation of cytotoxicity related to proteasome inhibition, in the presence of dopaminergic stimulation.

Systemic administration of a proteasome inhibitor does not cause nigrostriatal dopamine degeneration

Proteasomal dysfunction has been suggested to contribute to the degeneration of nigrostriatal dopamine neurons in Parkinson's disease. A recent study reported that systemic treatment of rats with the proteasome inhibitor Z-lle-Glu(OtBu)-Ala-Leu-al (PSI) causes a slowly progressive degeneration of nigrostriatal dopamine neurons, the presence of inclusion bodies in dopamine neurons, and motor impairment. We examined in vitro and in vivo the effects of PSI on nigrostriatal dopamine neurons. Mass spectrometric analysis was employed to verify the authenticity of the PSI compound. PSI was non-specifically toxic to neurons in ventral mesencephalic organotypic slice cultures, indicating that impairment of proteasome function in vitro is toxic. Moreover, systemic administration of PSI transiently decreased brain proteasome activity. Systemic treatment of rats with PSI did not, however, result in any biochemical or anatomical evidence of lesions of nigrostriatal dopamine neurons, nor were any changes in locomotor activity observed. These data suggest that systemic administration of proteasome inhibitors to normal adult rats does not reliably cause an animal model of parkinsonism.

Melatonin attenuates arsenite-induced apoptosis in rat brain: involvement of mitochondrial and endoplasmic reticulum pathways and aggregation of alpha-synuclein

In the present study, the protective effect of melatonin on sodium arsenite (arsenite)-induced apoptosis was investigated. Local infusion of arsenite elevated lipid peroxidation and depleted glutathione content in the infused substantia nigra (SN), as well as reduced striatal dopamine content. Systemic administration of melatonin diminished arsenite-induced oxidative injury. Furthermore, melatonin attenuated arsenite-induced increases in heat shock protein 70 and heme oxygenase-1 as well as phosphorylation of p38 mitogen-activated protein kinase and elevations in cyclooxygenase II and inducible nitric oxide synthase expression. Inhibition by melatonin of arsenite-induced apoptosis was determined by its attenuation of DNA fragmentation and terminal deoxytransferase-mediated dUTP-nick end labeling's positive cells in the infused SN of melatonin-treated rats. Melatonin reduced arsenite-induced apoptosis through mitochondrial and endoplasmic reticulum (ER) pathways. In the mitochondrial pathway, systemic melatonin inhibited arsenite-induced elevations in Bcl-2 and cytosolic cytochrome c as well as arsenite-induced reductions in procaspase-3 levels and elevations in active caspase-3 levels in the infused SN. Regarding the ER pathway, melatonin attenuated arsenite-induced elevations in activating transcription factor-4, CCAAT/enhancer binding protein (C/EBP) homologues protein, X-bon binding protein (XBP-1) and cytosolic immunoglobulin binding protein (BIP) as well as reductions in procaspase 12 levels. Moreover, aggregation of alpha-synuclein was reduced in the arsenite-infused SN of melatonin-treated rats. Our in vitro data showed that melatonin ameliorated arsenite-induced lipid peroxidation. Taken together, our data suggest that melatonin is neuroprotective against arsenite-induced oxidative injury in the nigrostriatal dopaminergic system of rat brain. Furthermore, the neuroprotective effects by melatonin on arsenite-induced apoptosis were mediated via inhibiting both mitochondrial and ER pathways. Accordingly, melatonin may be therapeutically useful for the treatment of arsenite-induced apoptosis in central nervous system.

Neurodegeneration of mouse nigrostriatal dopaminergic system induced by repeated oral administration of rotenone is prevented by 4-phenylbutyrate, a chemical chaperone

Parkinson's disease (PD) is a progressive neurodegenerative disorder that is primarily characterized by the degeneration of dopaminergic neurons in the nigrostriatal pathway. Previous studies have demonstrated that chronic systemic exposure of Lewis rats to rotenone produced many features of PD, and cerebral tauopathy was also detected in the case of severe weight loss. The present study was designed to assess the neurotoxicity of rotenone after daily oral administration for 28 days at several doses in C57BL/6 mice. In addition, we examined the protective effects of 4-phenylbutyrate (4-PBA) on nigral dopamine (DA) neurons in rotenone-treated mice. 4-PBA was injected intraperitoneally daily 30 min before each oral administration of rotenone. Chronic oral administration of rotenone at high doses induced specific nigrostriatal DA neurodegeneration, motor deficits and the up-regulation of alpha-synuclein in the surviving DA neurons. In contrast to the Lewis rat model, cerebral tauopathy was not detected in this mouse model. 4-PBA inhibited rotenone-induced neuronal death and decreased the protein level of alpha-synuclein. These results suggest that this rotenone mouse model may be useful for understanding the mechanism of DA neurodegeneration in PD, and that 4-PBA has a neuroprotective effect in the treatment of PD.

Proteasome Inhibition Induces Glutathione Synthesis and Protects Cells from Oxidative Stress

The cause of selective dopaminergic neuronal degeneration in Parkinson disease has still not been resolved, but it has been hypothesized that oxidative stress and the ubiquitin-proteasome system are important in the pathogenesis. In this report, we investigated the effect of proteasome inhibition on oxidative stress-induced cytotoxicity in PC12 cells, an in vitro model of Parkinson disease. Treatment with proteasome inhibitors provided significant protection against toxicity by 6-hydroxydopamine and H(2)O(2) in a concentration-dependent manner. The measurement of intracellular reactive oxygen species using 2',7'-dichlorofluorescein diacetate demonstrated that lactacystin, a proteasome inhibitor, significantly reduced 6-hydroxydopamineand H(2)O(2)-induced reactive oxygen species production. Proteasome inhibitors elevated the amount of glutathione and phosphorylated p38 mitogen-activated protein kinase (MAPK) prior to glutathione elevation. The treatment with lactacystin induced the nuclear translocation of NF-E2-related factor 2 (Nrf2) and increased the level of mRNA for gamma-glutamylcysteine synthetase, a rate-limiting enzyme in glutathione synthesis. Furthermore, SB203580, an inhibitor of p38 MAPK, abolished glutathione elevation and cytoprotection by lactacystin. These data suggest that proteasome inhibition afforded cytoprotection against oxidative stress by the elevation of glutathione content, and its elevation was mediated by p38 MAPK phosphorylation.

3-Hydroxymorphinan, a metabolite of dextromethorphan, protects nigrostriatal pathway against MPTP-elicited damage both in vivo and in vitro

We investigated the neuroprotective property of analogs of dextromethorphan (DM) in lipopolysaccharide (LPS) and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) models to identify neuroprotective drugs for Parkinson's disease (PD). In vivo studies showed that daily injections with DM analogs protected dopamine (DA) neurons in substantia nigra pars compacta and restored DA levels in striatum using two different models for PD. Of the five analogs studied, 3-hydroxymorphinan (3-HM), a metabolite of DM, was the most potent, and restored DA neuronal loss and DA depletion up to 90% of the controls. Behavioral studies showed an excellent correlation between potency for preventing toxin-induced decrease in motor activities and neuroprotective effects among the DM analogs studied, of which 3-HM was the most potent in attenuating behavioral damage. In vitro studies revealed two glia-dependent mechanisms for the neuroprotection by 3-HM. First, astroglia mediated the 3-HM-induced neurotrophic effect by increasing the gene expression of neurotrophic factors, which was associated with the increased acetylation of histone H3. Second, microglia participated in 3-HM-mediated neuroprotection by reducing MPTP-elicited reactive microgliosis as evidenced by the decreased production of reactive oxygen species. In summary, we show the potent neuroprotection by 3-HM in LPS and MPTP PD models investigated. With its high efficacy and low toxicity, 3-HM may be a novel therapy for PD.

Proteasome inhibitor model of Parkinson's disease in mice is confounded by neurotoxicity of the ethanol vehicle

Defects in the ubiquitin-proteasome system have been implicated in Parkinson's Disease (PD). Recently, a rat model of PD was developed using a synthetic proteasome inhibitor (PSI), (Z-lle-Glu(OtBu)-Ala-Leu-al). We attempted to transfer this model to mouse studies, where genetics can be more readily investigated due to the availability of genetically modified mice. We treated C57BL/6 (B6) mice with six intraperitoneal injections of 6 mg/kg PSI in 50 mul of 70% ethanol over a 2-week-period. We found significant decreases in nigrostriatal dopamine in PSI-treated mice compared with saline-treated mice. However, we observed similar decreases in the ethanol-treated vehicle control group. Administration of ethanol alone led to significant long-term alterations in dopamine levels. Ethanol significantly eclipses the effects of PSI in the dopamine system, and therefore is a confounding vehicle for this model.

Distribution of DJ-1, Parkinson's disease-related protein PARK7, and its alteration in 6-hydroxydopamine-treated hemiparkinsonian rat brain

DJ-1 has multiple functions and its dysfunction may be linked to the onset of familial Parkinson's disease PARK7. However, the function and distribution of DJ-1 is unclear. In this study, we determined DJ-1 distribution and change after intranigral injection of 6-hydroxydopamine (6-OHDA). Although distribution of DJ-1 immunoreactivity was not changed in cerebral cortex and striatum, 6-OHDA caused increase of DJ-1 in the particulate fraction and decrease in the cytosolic fraction in substantia nigra. At that time, DJ-1 shifted to acid forms. These results suggest that distributional changes, translocation, and acidic shift of DJ-1 may be compensatory responses to protect against 6-OHDA-induced oxidative stress.

PARK7 DJ-1 protects against degeneration of nigral dopaminergic neurons in Parkinson’s disease rat model

DJ-1 has recently been shown to be responsible for onset of familial Parkinson's disease (PD), PARK7. DJ-1 has been shown to play roles in transcriptional regulation and anti-oxidative stress, and loss of its function is thought to trigger onset of PD. In this study, a recombinant DJ-1 protein was administrated into the brain of PD model rats that had been injected to 6-hydroxydopamine (6-OHDA) in the left substantia nigra. PD phenotypes, including dopaminergic neuron death in the substantia nigra, decrease in dopamine, and dopamine transporter levels in the striatum, and motor abnormality, were dramatically improved by wild-type DJ-1 but not L166P DJ-1, a mutant form of DJ-1 found in PD patients. Furthermore, production of reactive oxygen species and cell death induced by 6-OHDA in SH-SY5Y cells and mesencephalic neurons were inhibited by addition of the recombinant DJ-1. These findings suggest that DJ-1 is a therapeutic target for PD.

Identification of gene expression changes in transgenic C. elegans overexpressing human alpha-synuclein

Alpha-synuclein containing cellular inclusions are a hallmark of Parkinson Disease, Lewy Body Dementia, and Multiple System Atrophy. A genome wide expression screen was performed in C. elegans overexpressing both wild-type and A53T human alpha-synuclein. 433 genes were up- and 67 genes down-regulated by statistical and fold change (> or <2) criteria. Gene ontology (GO) categories within the regulated gene lists indicated over-representation of development and reproduction, mitochondria, catalytic activity, and histone groups. Seven genes (pdr-1, ubc-7, pas-5, pas-7, pbs-4, RPT2, PSMD9) with function in the ubiquitin-proteasome system and 35 mitochondrial function genes were up-regulated. Nine genes that form histones H1, H2B, and H4 were down-regulated. These results demonstrate the effects of alpha-synuclein on proteasome and mitochondrial complex gene expression and provide further support for the role of these complexes in mediating neurotoxicity. The results also indicate an effect on nuclear protein genes that suggests a potential new avenue for investigation.

Nuclear factor-κB p65 and upregulation of interleukin-6 in retinal ischemia/reperfusion injury in rats

We previously demonstrated that endogenous interleukin-6 (IL-6) is upregulated and may be neuroprotective after retinal ischemia. The purpose of this study is to investigate the role of nuclear factor kappa-B (NF-kappaB) in regulating IL-6 expression after ischemia. NF-kappaB p65 mRNA levels were significantly elevated between 2 and 12 h after the insult. A high number of NF-kappaB p65 positive cells were detected in the inner retina at 12 h after ischemia. Activated nuclear NF-kappaB p65 and IL-6 were colocalized in cells, which were also marked by a microglial/phagocytic cell marker (ED1) in the inner retina. Carbobenzoxy-L-leucyl-L-leucyl-L-leucinal (MG-132, a proteasome inhibitor, which inhibits IkappaB degradation and hence prevents the activation and translocation of NF-kappaB into the nucleus) abolished the increase in NF-kappaB p65 mRNA levels after the insult, while there was no effect by helenalin (an inhibitor which inhibits NF-kappaB activity by alkylation of the p65 subunit, thereby blocking its binding to the target DNA). However, MG-132 and/or helenalin significantly diminished the increase in IL-6 mRNA levels after the insult. Small interfering RNAs (siRNAs, inhibit target gene expression through the sequence-specific destruction of the target messenger RNA) against NF-kappaB p65 significantly reduced the increase in NF-kappaB p65 mRNA levels as well as IL-6 mRNA levels after ischemia. The number of retinal ganglion cells (RGCs) was also significantly decreased using the inhibitors of NF-kappaB compared with those of the controls after ischemia. These findings support the hypothesis that upregulation of endogenous retinal IL-6 in retinal I/R injury in microglial/phagocytic cells is controlled predominantly by NF-kappaB p65.

The proteasome in Alzheimer's disease and Parkinson's disease: lessons from ubiquitin B+1

Ubiquitin-containing cellular inclusions are characteristic of major neurodegenerative diseases and suggest an involvement of the ubiquitin-proteasome system. The frameshifted form of ubiquitin has proved to be a valuable tool for studying the role of the ubiquitin-proteasome system. It is an endogenous reporter for proteasome activity in human pathology but it is also capable of inhibiting proteasomal degradation. Current studies have revealed that the frameshifted form of ubiquitin accumulates in the brains of patients with Alzheimer's disease but not in those with Parkinson's disease.

Serofendic acid prevents 6-hydroxydopamine-induced nigral neurodegeneration and drug-induced rotational asymmetry in hemi-parkinsonian rats

Serofendic acid was recently identified as a neuroprotective factor from fetal calf serum. This study was designed to evaluate the neuroprotective effects of an intranigral microinjection of serofendic acid based on behavioral, neurochemical and histochemical studies in hemi-parkinsonian rats using 6-hydroxydopamine (6-OHDA). Rats were injected with 6-OHDA in the presence or absence of serofendic acid, or were treated with serofendic acid on the same lateral side, at 12, 24 or 72 h after 6-OHDA lesion. Intranigral injection of 6-OHDA alone induced a massive loss of tyrosine hydroxylase (TH)-immunopositive neurons in the substantia nigra pars compacta (SNpc). Either simultaneous or 12 h post-administration of serofendic acid significantly prevented both dopaminergic neurodegeneration and drug-induced rotational asymmetry. Immunoreactivities for oxidative stress markers, such as 3-nitrotyrosine (3-NT) and 4-hydroxy-2-nonenal (4-HNE), were markedly detected in the SNpc of rats injected with 6-OHDA alone. These immunoreactivities were markedly suppressed by the co-administration of serofendic acid, similar to the results in vehicle-treated control rats. In addition, serofendic acid inhibited 6-OHDA-induced alpha-synuclein expression and glial activation in the SNpc. These results suggest that serofendic acid protects against 6-OHDA-induced SNpc dopaminergic neurodegeneration in a rat model of Parkinson's disease.

Does Proteosome Inhibition Decrease or Accelerate Toxin-Induced Dopaminergic Neurodegeneration?

Parkinson's disease (PD) is pathologically characterized by dopaminergic (DA) cell death and the presence of Lewy bodies (LB) in the brain. alpha-Synuclein (alpha-syn) and ubiquitin (Ub) are the major components of LB, however, the process of their accumulation and their relationship to DA cell loss has not yet been resolved. Now, in this journal, Inden et al. showed the protective effect of proteasome inhibitors (PSI) on DA cell death in the rat PD model using 6-hydroxyl dopamine (6-OHDA). Co-administration of PSI, lactacystin, or MG-132 significantly prevented the nigral degeneration and apomorphine-induced rotational asymmetry of the model with increased appearance of alpha-syn- and Ub-positive inclusions in the substantia nigra. This study indicates that in their model, accelerated formation of inclusions via proteasome inhibition protects against DA cell death. Previous literature linked the impairments or inhibitions of the ubiquitin-proteasome system (UPS) and DA cell death. However, this report implies that the relationship between the UPS and the pathogenesis of PD may be more complex than we thought.