Failure of the ubiquitin-proteasome system in Parkinson's disease

Oxidative stress resistance in Deinococcus radiodurans

Deinococcus radiodurans is a robust bacterium best known for its capacity to repair massive DNA damage efficiently and accurately. It is extremely resistant to many DNA-damaging agents, including ionizing radiation and UV radiation (100 to 295 nm), desiccation, and mitomycin C, which induce oxidative damage not only to DNA but also to all cellular macromolecules via the production of reactive oxygen species. The extreme resilience of D. radiodurans to oxidative stress is imparted synergistically by an efficient protection of proteins against oxidative stress and an efficient DNA repair mechanism, enhanced by functional redundancies in both systems. D. radiodurans assets for the prevention of and recovery from oxidative stress are extensively reviewed here. Radiation- and desiccation-resistant bacteria such as D. radiodurans have substantially lower protein oxidation levels than do sensitive bacteria but have similar yields of DNA double-strand breaks. These findings challenge the concept of DNA as the primary target of radiation toxicity while advancing protein damage, and the protection of proteins against oxidative damage, as a new paradigm of radiation toxicity and survival. The protection of DNA repair and other proteins against oxidative damage is imparted by enzymatic and nonenzymatic antioxidant defense systems dominated by divalent manganese complexes. Given that oxidative stress caused by the accumulation of reactive oxygen species is associated with aging and cancer, a comprehensive outlook on D. radiodurans strategies of combating oxidative stress may open new avenues for antiaging and anticancer treatments. The study of the antioxidation protection in D. radiodurans is therefore of considerable potential interest for medicine and public health.

Glyceraldehyde-3-phosphate dehydrogenase: activity inhibition and protein overexpression in rotenone models for Parkinson's disease

Rotenone, a widely used pesticide and an environmental risk factor for Parkinson's disease (PD), induces nigrostriatal injury, Lewy body-like inclusions, and Parkinsonian symptoms in rat models for PD. Our previous data indicated that glyceraldehyde-3-phosphate dehydrogenase (GAPDH) overexpression and glycolytic inhibition were co-current in rotenone-induced PC12 (rat adrenal pheochromocytoma cells) cell death. However, whether GAPDH overexpression plays any role in dopaminergic neurodegeneration in vivo remains unknown. In this study, we have found that GAPDH overexpression and GAPDH-positive Lewy body-like aggregates in nigral dopaminergic neurons while nigral GAPDH glycolytic activity decreases in rotenone-based PD animal models. Furthermore, GAPDH knockdown reduces rotenone toxicity significantly in PC12. These in vitro and in vivo data suggest that GAPDH contributes to the pathogenesis of Parkinson's disease, possibly representing a new molecular target for neuroprotective strategies and alternative therapies for PD.

Pros and cons of a prion-like pathogenesis in Parkinson's disease

Background

Parkinson's disease (PD) is a slowly progressive neurodegenerative disorder which affects widespread areas of the brainstem, basal ganglia and cerebral cortex. A number of proteins are known to accumulate in parkinsonian brains including ubiquitin and α-synuclein. Prion diseases are sporadic, genetic or infectious disorders with various clinical and histopathological features caused by prion proteins as infectious proteinaceous particles transmitting a misfolded protein configuration through brain tissue. The most important form is Creutzfeldt-Jakob disease which is associated with a self-propagating pathological precursor form of the prion protein that is physiologically widely distributed in the central nervous system.

Discussion

It has recently been found that α-synuclein may behave similarly to the prion precursor and propagate between cells. The post-mortem proof of α-synuclein containing Lewy bodies in embryonic dopamine cells transplants in PD patient suggests that the misfolded protein might be transmitted from the diseased host to donor neurons reminiscent of prion behavior. The involvement of the basal ganglia and brainstem in the degenerative process are other congruencies between Parkinson's and Creutzfeldt-Jakob disease. However, a number of issues advise caution before categorizing Parkinson's disease as a prion disorder, because clinical appearance, brain imaging, cerebrospinal fluid and neuropathological findings exhibit fundamental differences between both disease entities. Most of all, infectiousness, a crucial hallmark of prion diseases, has never been observed in PD so far. Moreover, the cellular propagation of the prion protein has not been clearly defined and it is, therefore, difficult to assess the molecular similarities between the two disease entities.

Summary

At the current state of knowledge, the molecular pathways of transmissible pathogenic proteins are not yet fully understood. Their exact involvement in the pathophysiology of prion disorders and neurodegenerative diseases has to be further investigated in order to elucidate a possible overlap between both disease categories that are currently regarded as distinct entities.

Interference of alpha-synuclein with cAMP/PKA-dependent CREB signaling for tyrosine hydroxylase gene expression in SK-N-BE(2)C cells

Alpha-synuclein (α-SYN) is a small and highly conserved presynaptic protein that is implicated in both normal brain function and the pathogenesis of neurodegenerative diseases. Although the physiological function of α-SYN has not been fully evaluated, several lines of evidence suggest that it plays an important role in the regulation of dopamine homeostasis in the brain. Early studies have demonstrated that interaction of α-SYN and tyrosine hydroxylase (TH), a rate-limiting enzyme in dopamine synthesis, is functionally significant for dopaminergic neurotransmission and the pathophysiology of Parkinson's disease. In the present study, we would like to evaluate whether overexpression of wild-type or mutant α-SYN might affect cAMP/PKA-dependent TH activation in DA-producing SK-N-BE(2)C cells. Here we show that wild-type and mutant A30P and A53T α-SYN attenuate forskolin-induced TH up-regulation, but do not suppress TH basal expression in SK-N-BE(2)C cells. Forskolin-induced increase in TH promoter activity and CRE-dependent transcription are significantly suppressed in α-SYN-overexpressing cells. Alpha-SYN enters the nucleus, but does not bind to CREB or interfere with forskolin-induced CREB phosphorylation. These data indicate that elevated levels of α-SYN due to a specific disease or the normal aging process could be associated with dopaminergic neuronal dysfunction through interference with TH regulation.

The role of ubiquitin-proteasome system in ageing

Maintenance of cellular homeostasis influences ageing and it is determined by several factors, including efficient proteolysis of damaged proteins. The ubiquitin-proteasome system is the major protein degradation pathway in the cell. Specifically, the proteasome is responsible for clearance of abnormal, denatured or in general damaged proteins as well as for the regulated degradation of short-lived proteins. In this review the involvement of the ubiquitin-proteasome pathway in protein degradation at different levels of cellular life is discussed in relation with ageing. Though the exact underlying mechanism is unclear, an age-related decrease in proteasome activity weakens cellular capacity to remove oxidatively modified proteins and favours the development of diseases. Up-regulation of proteasome activity is characteristic of muscle wasting conditions, but may not be rate limiting. Meanwhile, enhanced presence of immunoproteasomes in ageing brain and muscle tissue could reflect a persistent inflammatory defence and anti-stress mechanism. Insulin/IGF-1 signalling regulates ageing in worms, flies and mammals. The insulin/IGF-1 receptor inhibits the forkhead transcription factor, FoxO through activating a cascade of conserved kinases. Longevity increases when FoxO becomes activated in response to reduced insulin/IGF-1 signalling. The ubiquitin-proteasome system plays a major role in signal transduction associated with stress and ageing. The understanding of specific proteolytic targeting paves the way for a new generation of active molecules that may control particular steps of normal and pathological ageing.

Loss of nuclear factor E2-related factor 1 in the brain leads to dysregulation of proteasome gene expression and neurodegeneration

The ubiquitin-proteasome pathway plays an important role in the pathogenesis of neurodegeneration, but mechanisms controlling expression of components in this pathway remain poorly understood. Nuclear factor E2-related factor 1 (Nrf1) transcription factor has been shown to regulate expression of antioxidant and cytoprotective genes. To determine the function of Nrf1 in the brain, mice with a late-stage deletion of Nrf1 in neuronal cells were generated. Loss of Nrf1 leads to impaired proteasome function and neurodegeneration. Gene expression profiling and RT-PCR analysis revealed a coordinate down-regulation of various proteasomal genes including PsmB6, which encodes a catalytic subunit of the proteasome. Transcriptional analysis and chromatin immunoprecipitation experiments demonstrated that PsmB6 is an Nrf1 target gene. These findings reveal Nrf1 as a key transcriptional regulator required for the expression of proteasomal genes in neurons and suggest that perturbations of Nrf1 function may contribute to the pathogenesis of neurodegenerative diseases.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry combined with magnetic beads for detecting serum protein biomarkers in parkinson's disease

BACKGROUND

Biomarkers for neurodegenerative diseases are essential to facilitate disease diagnosis. Application of proteomics has greatly hastened the search for novel biomarkers. In this study, new potential biomarkers were discovered, and a diagnostic pattern was established for idiopathic Parkinson's disease (PD) by using proteomic technology.

METHODS

Serum proteins from PD patients and controls were captured by magnetic bead-based weak cation exchange. The molecular weight of the proteins in bead-binding fraction was detected by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Biomarker Wizard 3.1 and Biomarker Patterns Software were used for data analysis and constructing a model of biomarkers. A blinded testing set was used to validate the model.

RESULTS

A total of 17 discriminating m/z peaks related to PD were identified. The model based on the 5 biomarkers generated an excellent separation between PD and healthy controls with 98.36% for the sensitivity and 83.05% for the specificity. Blind test data demonstrated the model could recognize patients with PD with a sensitivity of 85.0% and a specificity of 70.0%.

CONCLUSIONS

The preliminary data suggested a potential application of MALDI-TOF-MS combined with magnetic beads. The model comprising 5 promising biomarkers can differentiate individuals with PD and the healthy subjects precisely.

Inhibition of all-trans-retinoic acid-induced proteasome activation potentiates the differentiating effect of retinoid in acute myeloid leukemia cells

All-trans retinoic acid (ATRA) is nowadays considered to be the sole efficient agent for differentiation-based therapy in leukemia; however, the mechanisms of ATRA's biological effects remain largely unknown. Here we first reported that ATRA-induced myeloid leukemia differentiation was accompanied with the increased level of ubiquitin-protein conjugates and the upregulation of proteasome activity. To explore the functional role of the activated proteasome in retinoic acid (RA) signaling, the effects of proteasome inhibitors on RA-induced cell differentiation were determined. Our results demonstrated that inhibition of ATRA-elevated proteasome activity obviously promoted the myeloid maturation program triggered by ATRA, suggesting that the overactivated proteasome is not beneficial for ATRA's effects. Further studies demonstrated that the synergistic differentiating effects of ATRA and proteasome inhibitors might be associated with the protection of retinoic acid receptor alpha (RARα) from degradation by the ubiquitin-proteasome pathway (UPP). Moreover, the accumulated RARα was able to enhance the transcription of its target gene, which might also contribute to the enhanced differentiation of leukemia cells. Together, by linking the UPP to ATRA-dependent signaling, our data provide a novel insight into studying the mechanisms of ATRA-elicited cellular effects and imply the possibility of combination of ATRA and proteasome inhibitors in leukemia therapy.

Up-regulation of endoplasmic reticulum stress-related genes during the early phase of treatment of cultured cortical neurons by the proteasomal inhibitor lactacystin

Inhibition of proteasome degradation pathway has been implicated in neuronal cell death leading to neurodegenerative diseases such as Parkinson's disease and Alzheimer's disease. We and others demonstrated that treatment of cortical neurons with the proteasomal inhibitor lactacystin leads to apoptosis. We discovered by microarray analysis that lactacystin treatment modulates the expression of both potentially neuroprotective as well as pro-apoptotic genes in neurons. However, the significance of the genes which upon transcriptional modulation contributed to proteasomal inhibition-induced apoptosis, remained unidentified. By employing microarray analysis to decipher the time-dependent changes in transcription of these genes in cultured cortical neurons, we discovered different groups of genes were transcriptionally regulated in the early and late phase of lactacystin-induced cell death. In the early phase, several neuroprotective genes such as those encoding the proteasome subunits and ubiquitin-associated enzymes, as well as the heat-shock proteins (HSP) were up-regulated. However, the pro-apoptotic endoplasmic reticulum (ER) stress-associated genes were also up-regulated at the early phase of lactacystin-induced neuronal cell death. In the late phase, genes encoding antioxidants and calcium-binding proteins were up-regulated while those associated with cholesterol biosynthesis were down-regulated. The data suggest that ER stress may participate in mediating the apoptotic responses induced by proteasomal inhibition. The up-regulation of the neuroprotective antioxidant genes and calcium-binding protein genes and down-regulation of the cholesterol biosynthesis genes in the later phase are likely consequences of stimulation of the pro-apoptotic signaling pathways in the early phase of lactacystin treatment.

Mitochondrial abnormalities in the putamen in Parkinson's disease dyskinesia

Prolonged treatment of Parkinson's disease (PD) with levodopa leads to disabling side effects collectively referred to as 'dyskinesias'. We hypothesized that bioenergetic function in the putamen might play a crucial role in the development of dyskinesias. To test this hypothesis, we used post mortem samples of the human putamen and applied real time-PCR approaches and gene expression microarrays. We found that mitochondrial DNA (mtDNA) levels are decreased in patients who have developed dyskinesias, and mtDNA damage is concomitantly increased. These pathologies were not observed in PD subjects without signs of dyskinesias. The group of nuclear mRNA transcripts coding for the proteins of the mitochondrial electron transfer chain was decreased in patients with dyskinesias to a larger extent than in patients who had not developed dyskinesias. To examine whether dopamine fluctuations affect mtDNA levels in dopaminoceptive neurons, rat striatal neurons in culture were repeatedly exposed to levodopa, dopamine or their metabolites. MtDNA levels were reduced after treatment with dopamine, but not after treatment with dopamine metabolites. Levodopa led to an increase in mtDNA levels. We conclude that mitochondrial susceptibility in the putamen plays a role in the development of dyskinesias.

Vulnerability of mesostriatal dopaminergic neurons in Parkinson's disease

The term vulnerability was first associated with the midbrain dopaminergic neurons 85 years ago, before they were identified as monoaminergic neurons, when Foix and Nicolesco (1925) reported the loss of neuromelanin containing neurons in the midbrain of patients with post-encephalitic Parkinson's disease (PD). A few years later, Hassler (1938) showed that degeneration is more intense in the ventral tier of the substantia nigra compacta than in its dorsal tier and the ventral tegmental area (VTA), outlining the concept of differential vulnerability of midbrain dopaminergic (DA-) neurons. Nowadays, we know that other neuronal groups degenerate in PD, but the massive loss of nigral DA-cells is its pathological hallmark, having a pivotal position in the pathophysiology of the disease as it is responsible for the motor symptoms. Data from humans as well as cellular and animal models indicate that DA-cell degeneration is a complex process, probably precipitated by the convergence of different risk factors, mediated by oxidative stress, and involving pathogenic factors arising within the DA-neuron (intrinsic factors), and from its environment and distant interconnected brain regions (extrinsic factors). In light of current data, intrinsic factors seem to be preferentially involved in the first steps of the degenerative process, and extrinsic factors in its progression. A controversial issue is the relative weight of the impairment of common cell functions, such as energy metabolism and proteostasis, and specific dopaminergic functions, such as pacemaking activity and DA handling, in the pathogenesis of DA-cell degeneration. Here we will review the current knowledge about the relevance of these factors at the beginning and during the progression of PD, and in the differential vulnerability of midbrain DA-cells.

α-Synuclein impairs macroautophagy: implications for Parkinson's disease

Parkinson's disease (PD) is characterized pathologically by intraneuronal inclusions called Lewy bodies, largely comprised of α-synuclein. Multiplication of the α-synuclein gene locus increases α-synuclein expression and causes PD. Thus, overexpression of wild-type α-synuclein is toxic. In this study, we demonstrate that α-synuclein overexpression impairs macroautophagy in mammalian cells and in transgenic mice. Our data show that α-synuclein compromises autophagy via Rab1a inhibition and Rab1a overexpression rescues the autophagy defect caused by α-synuclein. Inhibition of autophagy by α-synuclein overexpression or Rab1a knockdown causes mislocalization of the autophagy protein, Atg9, and decreases omegasome formation. Rab1a, α-synuclein, and Atg9 all regulate formation of the omegasome, which marks autophagosome precursors.

Pathological considerations in the treatment of Parkinson's disease: more than just a wiring diagram

Parkinson's disease (PD) represents a common but challenging condition in which an increasing number of therapeutic options have evolved over the course of the last 50 years. The introduction of dopaminergic therapies has dramatically improved outcomes but life expectancies remain significantly curtailed. Currently, all available treatment options are directed towards the amelioration of symptoms. However, it is hoped that a greater understanding of the distinctive pathology underlying PD might offer some novel therapeutic approaches. The identification of degeneration within the nigrostriatal tract as the most prominent pathological process in PD has led to the development of a number of therapies. However, despite initially good symptomatic control it has become clear that the longer-term use of these medications is associated with a number of debilitating motor complications. The management of these drug-related issues has necessitated a further tier of therapeutic options based largely on a greater understanding of the basal ganglia circuitry involved. Indeed, surgical interventions targeting these neural circuits have provided increased control of motor symptoms in patients with advanced disease, however, such techniques still fail to slow or reverse the disease. To this end, a number of novel approaches focussed on restoration or repair of the diseased brain have received increasing attention. Nevertheless, there are multiple symptoms that are unresponsive to any of these therapies, highlighting the involvement of other neurotransmitter systems and the complexities of the disease beyond the basal ganglia circuitry. An appreciation of the ongoing neurodegenerative processes at the core of PD and the burden of disease associated with them, emphasises the need for increased research into more effective and comprehensive treatment methodologies.

Neuromelanin selectively induces apoptosis in dopaminergic SH-SY5Y cells by deglutathionylation in mitochondria: involvement of the protein and melanin component

Parkinson's disease (PD) is characterized by selective depletion of nigral dopamine (DA) neurons containing neuromelanin (NM), suggesting the involvement of NM in the pathogenesis. This study reports induction of apoptosis by NM in SH-SY5Y cells, whereas protease-K-treated NM, synthesized DA- and cysteinyl dopamine melanin showed much less cytotoxicity. Cell death was mediated by mitochondria-mediated apoptotic pathway, namely collapse of mitochondrial membrane potential, release of cytochrome c, and activation of caspase 3, but Bcl-2 over-expression did not suppress apoptosis. NM increased sulfhydryl content in mitochondria, and a major part of it was identified as GSH, whereas dopamine melanin significantly reduced sulfhydryl levels. Western blot analysis for protein-bound GSH demonstrated that only NM reduced S-glutathionylated proteins in mitochondria and dissociated macromolecular structure of complex I. Reactive oxygen and nitrogen species were required for the deglutathionylation by NM, which antioxidants reduced significantly with prevention of apoptosis. These results suggest that NM may be related to cell death of DA neurons in PD and aging through regulation of mitochondrial redox state and S-glutathionylation, for which NM-associated protein is absolutely required. The novel function of NM is discussed in relation to the pathogenesis of PD.

Tryptophan, Neurodegeneration and HIV-Associated Neurocognitive Disorder

This review presents an up-to-date assessment of the role of the tryptophan metabolic and catabolic pathways in neurodegenerative disease and HIV-associated neurocognitive disorder. The kynurenine pathway and the effects of each of its enzymes and products are reviewed. The differential expression of the kynurenine pathway in cells within the brain, including inflammatory cells, is explored given the increasing recognition of the importance of inflammation in neurodegenerative disease. An overview of common mechanisms of neurodegeneration is presented before a review and discussion of the evidence for a pathogenetic role of the kynurenine pathway in Alzheimer's disease, HIV-associated neurocognitive disorder, Huntington's disease, motor neurone disease, and Parkinson's disease.

Estrogen actions in the brain and the basis for differential action in men and women: a case for sex-specific medicines

The classic view of estrogen actions in the brain was confined to regulation of ovulation and reproductive behavior in the female of all mammalian species studied, including humans. Burgeoning evidence now documents profound effects of estrogens on learning, memory, and mood as well as neurodevelopmental and neurodegenerative processes. Most data derive from studies in females, but there is mounting recognition that estrogens play important roles in the male brain, where they can be generated from circulating testosterone by local aromatase enzymes or synthesized de novo by neurons and glia. Estrogen-based therapy therefore holds considerable promise for brain disorders that affect both men and women. However, as investigations are beginning to consider the role of estrogens in the male brain more carefully, it emerges that they have different, even opposite, effects as well as similar effects in male and female brains. This review focuses on these differences, including sex dimorphisms in the ability of estradiol to influence synaptic plasticity, neurotransmission, neurodegeneration, and cognition, which, we argue, are due in a large part to sex differences in the organization of the underlying circuitry. There are notable sex differences in the incidence and manifestations of virtually all central nervous system disorders, including neurodegenerative disease (Parkinson's and Alzheimer's), drug abuse, anxiety, and depression. Understanding the cellular and molecular basis of sex differences in brain physiology and responses to estrogen and estrogen mimics is, therefore, vitally important for understanding the nature and origins of sex-specific pathological conditions and for designing novel hormone-based therapeutic agents that will have optimal effectiveness in men or women.

BimEL as a possible molecular link between proteasome dysfunction and cell death induced by mutant huntingtin

Huntington's disease (HD) is a devastating neurodegenerative disorder caused by an expanded polyglutamine repeat within the N-terminus of the huntingtin protein. It is characterized by a selective loss of medium spiny neurons in the striatum. It has been suggested that impaired proteasome function and endoplasmic reticulum (ER) stress play important roles in mutant huntingtin (mHtt)-induced cell death. However, the molecular link involved is poorly understood. In the present study, we identified the essential role of the extra long form of Bim (Bcl-2 interacting mediator of cell death), BimEL, in mHtt-induced cell death. BimEL protein expression level was significantly increased in cell lines expressing the N-terminus of mHtt and in a mouse model of HD. Although quantitative RT-PCR analysis indicated that BimEL mRNA was increased in cells expressing mHtt, we provided evidence showing that, at the post-translational level, phosphorylation of BimEL played a more important role in regulating BimEL expression. Up-regulation of BimEL facilitated the translocation of Bax to the mitochondrial membrane, which further led to cytochrome c release and cell death. On the other hand, knocking down BimEL expression prevented mHtt-induced cell death. Taken together, these findings suggest that BimEL is a key element in regulating mHtt-induced cell death. A model depicting the role of BimEL in linking mHtt-induced ER stress and proteasome dysfunction to cell death is proposed.

Loss of leucine-rich repeat kinase 2 causes impairment of protein degradation pathways, accumulation of alpha-synuclein, and apoptotic cell death in aged mice

Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most common genetic cause of Parkinson's disease. LRRK2 is a large protein containing a small GTPase domain and a kinase domain, but its physiological role is unknown. To identify the normal function of LRRK2 in vivo, we generated two independent lines of germ-line deletion mice. The dopaminergic system of LRRK2(-/-) mice appears normal, and numbers of dopaminergic neurons and levels of striatal dopamine are unchanged. However, LRRK2(-/-) kidneys, which suffer the greatest loss of LRRK compared with other organs, develop striking accumulation and aggregation of alpha-synuclein and ubiquitinated proteins at 20 months of age. The autophagy-lysosomal pathway is also impaired in the absence of LRRK2, as indicated by accumulation of lipofuscin granules as well as altered levels of LC3-II and p62. Furthermore, loss of LRRK2 dramatically increases apoptotic cell death, inflammatory responses, and oxidative damage. Collectively, our findings show that LRRK2 plays an essential and unexpected role in the regulation of protein homeostasis during aging, and suggest that LRRK2 mutations may cause Parkinson's disease and cell death via impairment of protein degradation pathways, leading to alpha-synuclein accumulation and aggregation over time.

Effect of the overexpression of mutant ubiquitin (K48R) on the cellular response induced by 4-hydroxy-2,3-trans-nonenal, an end-product of lipid peroxidation

Impairment of the ubiquitin-proteasome system (UPS) for degrading abnormal proteins leads to protein aggregates and increased protein oxidation/nitration. This study was performed to show that interference with polyubiquitination in the presence of 4-hydroxy-2,3-trans-nonenal (HNE) has similar consequences. Levels of polyubiquitin chains were not increased in NT-2 and SK-N-MC cells overexpressing a dominant-negative mutant form of ubiquitin (K48R) in response to HNE compared to wild-type transfectants. Increased oxidative (GSH, protein carbonyls and lipid peroxidation) and nitrative damage (nitric oxide production and elevated protein nitration) were aggravated in the mutant transfectants. These data show that initial oxidative/nitrative damage (due to HNE) and interference with ubiquitination (induced by mutant ubiquitin or HNE) can cause common characteristics of neurodegenerative diseases. These data suggest that impairment of the UPS at different levels may be a common mechanism in neurodegeneration and that more such defects remain to be identified.

TGF-beta 1 enhances neurite outgrowth via regulation of proteasome function and EFABP

Malfunction of the ubiquitin-proteasome system has been implicated as a causal factor in the pathogenesis of aggregation-related disorders, e.g. Parkinson's disease. We show here that Transforming growth factor-beta 1 (TGF-beta), a multifunctional cytokine and trophic factor for dopaminergic (DAergic) neurons modulates proteasome function in primary midbrain neurons. TGF-beta differentially inhibited proteasomal subactivities with a most pronounced time-dependent inhibition of the peptidyl-glutamyl peptide hydrolyzing-like and chymotrypsin-like subactivity. Regulation of proteasomal activity could be specifically quantified in the DAergic subpopulation. Protein blot analysis revealed an accumulation of ubiquitinated proteins after TGF-beta treatment. The identity of these enriched proteins was further analyzed by 2D-gel electrophoresis and mass spectrometry. We found epidermal fatty acid binding protein (EFABP) to be strongly increased and ubiquitinated after TGF-beta treatment and confirmed this finding by co-immunoprecipitation. While application of TGF-beta increased neurite regeneration in a scratch lesion model, downregulation of EFABP by siRNA significantly decreased this effect. We thus postulate that a differential regulation of proteasomal function, as demonstrated for TGF-beta, can result in an enrichment of proteins, such as EFABP, that mediate physiological functions, such as neurite regeneration.

Stable isotope labeling and label-free proteomics of Drosophila parkin null mutants

Parkinson's disease (PD) is characterized by loss of dopaminergic neurons in the substantia nigra and formation of intracytoplasmic Lewy bodies (LBs). Loss-of-function mutations in parkin which encodes an E3 ubiquitin protein ligase contribute to a predominant cause of a familial form of PD termed autosomal recessive juvenile Parkinsonism (AR-JP). Drosophila parkin null mutants display muscle degeneration and mitochondrial dysfunction, providing an animal model to study Parkin-associated molecular pathways in PD. To define protein alterations involved in Parkin pathogenesis, we performed quantitative proteomic analyses of Drosophila parkin null mutants and age-matched controls utilizing both global internal standard technology (GIST) and extracted ion chromatogram peak area (XICPA) label-free approaches. A total of 375 proteins were quantified with a minimum of two peptide identifications from the combination of the XICPA and GIST measurements applied to two independent biological replicates. Sixteen proteins exhibited significant alteration. Seven of the dysregulated proteins are involved in energy metabolism, of which six were down-regulated. All five proteins involved in transporter activity exhibited higher levels, of which larval serum protein 1alpha, larval serum protein 1beta, larval serum protein 1gamma, and fat body protein 1 showed >10-fold up-regulation and substantially higher level of fat body protein 1 was confirmed by Western blot analysis. These findings suggest that abnormalities in energy metabolism and protein transporter activity pathways may be associated with the pathogenesis of Parkin-associated AR-JP.

Biochemical and pathological correlates of cognitive and behavioural change in DLB/PDD

Dementia with Lewy bodies (DLB) and Parkinson's disease dementia (PDD) are second only to Alzheimer's disease (AD) in frequency. In particular it is evident that up to 80% of people with PD will develop dementia towards the end of their life. While the neurobiology of movement disorder has been well studied in PD, much less attention has been given to mechanisms underlying the cognitive and behavioural symptoms associated with DLB and PDD. To date, the best correlate of cognitive impairment appears to be cortical Lewy bodies; however, new emphasis has been placed on small aggregates of synuclein. Furthermore, very few studies have attempted to investigate the neurochemical correlates of behavioural disorders in DLB/PDD and whether these are similar or distinct from AD. Aggregated alpha-synuclein forms the core component of Lewy bodies, a major pathological feature of Parkinson's-related conditions. The 26S proteasome is an ATP-dependent protease that catalyses the breakdown of alpha-synuclein. Previous studies have implicated alterations in the proteasome in PD. Furthermore, proteasome inhibitors have been reported to induce alpha-synuclein aggregation and Lewy body-like inclusions, resulting in neuronal loss both in vitro and in vivo. Our preliminary results indicate that selective alterations in the expression of proteosome sub-units are a feature of both DLB and PDD, while changes in activity are restricted to PDD. Depression is a common symptom in DLB/PDD, yet the evidence base for standard treatment with SSRIs is limited. In contrast to previous studies of AD, our results indicate that there is no association between depression and the 5-HT transporter, while there was a significant increase in the number of 5-HT1A receptors in those DLB/PDD patients with depression. These data may provide an insight into the lack of success of current treatments and suggest alternative approaches.

Accumulation of phosphorylated tyrosine hydroxylase into insoluble protein aggregates by inhibition of an ubiquitin-proteasome system in PC12D cells

Tyrosine hydroxylase (TH) is a rate-limiting enzyme for the biosynthesis of catecholamines including dopamine. The relationship between proteasomal dysfunction and the etiology of Parkinson's disease has been suggested, but it is unknown if TH protein is affected by proteasomal dysfunctions. Here, we examined the effect of inhibition of ubiquitin-proteasomal pathway on biochemical characteristics of TH protein in the neuronal cells. Inhibition of 20S or 26S proteasome by proteasome inhibitor I, or MG-132 in NGF-differentiated PC12D cells induced dot-like immunoreactivities with the anti-(40)Ser-phosphorylated TH (p40-TH) antibody. These dots were tightly co-localized with ubiquitin and positive to Thioflavine-S staining. These dot-like immunoreactivities were not obvious when immunostaining was performed against total-TH or choline acetyltransferase. Western blotting analysis showed time-dependent increase of p40-TH in the Triton-insoluble fractions. We also examined the effect of okadaic acid, an inhibitor of protein phosphatase 2A, which is a phosphatase acting on p40-TH. Okadaic acid increased the amount of insoluble p40-TH. These data suggest that p40-TH is prone to be insolubilized and aggregated by dysfunction of an ubiquitin-proteasome system in PC12D cells.

Reciprocal effects of alpha-synuclein overexpression and proteasome inhibition in neuronal cells and tissue

Defects in the 20S/26S proteasome and conformational changes in alpha-synuclein (alpha-syn) are implicated in the development of sporadic and familial cases of PD. The objective of this study was to evaluate whether alpha-syn affects proteolysis by the proteasome and, reciprocally, whether proteasome inhibition affects alpha-syn solubility and localization. Although alpha-syn directly inhibited purified 20S proteasomes reversibly in vitro, its overexpression in neuroblastoma (SH-SY5Y and SK-N-BE), embryonic kidney (HEK293) cells, or mouse brain did not affect proteasome activity. Proteasome inhibition with MG132 and epoxomicin in SH-SY5Y cells failed to induce alpha-syn aggregation, although it increased membrane bound forms of endogenous and overexpressed wild-type, but not mutant, alpha-syn. Concomitantly this treatment generated cytoplasmic alpha-syn inclusions devoid of polyubiquitin in a small percentage of cells. The combination of proteasome inhibition with serum deprivation, which induced oxidative stress and autophagy, caused the appearance of high molecular weight alpha-syn species, such as those found in Lewy bodies. Our data suggest that high concentrations of alpha-syn do not affect proteasome function in vivo, whereas proteasome inhibition can modify synuclein solubility, most prominently under conditions of cell stress which occur during aging. These results have implications for the convergence of age-related oxidative stress and impaired protein degradation in neurodegeneration.

A role for a novel protein, nucleolin, in Parkinson's disease

Although much has been learned in the last few decades concerning the molecular mechanisms and pathways associated with the development of familial as well as sporadic Parkinson disease (PD), the precise mechanisms and specific proteins responsible for mediating these effects remain to be elucidated. Thus, the identification and biological evaluation of novel proteins involved in these pathways is critical to providing a more comprehensive understanding of PD pathogenesis. Previously, in a cellular model of PD, we identified nucleolin as a protein interacting with alpha-synuclein and DJ-1, two critical proteins involved in PD pathogenesis. In our current study, we found the expression levels of nucleolin were dramatically reduced in the substantia nigra pars compacta of human PD subjects, compared with controls. Furthermore, manipulation of nucleolin in an in vitro model of PD resulted in significant alterations in the generation of oxidative stress as well as proteasomal inhibition following rotenone exposure. Interestingly, nucleolin expression did not influence mitochondrial complex I activity, suggesting a selective specificity for oxidative stress and proteasomal pathways.

Proteomics in human Parkinson's disease research

During the last decades, considerable advances in the understanding of specific mechanisms underlying neurodegeneration in Parkinson's disease have been achieved, yet neither definite etiology nor unifying sequence of molecular events has been formally established. Current unmet needs in Parkinson's disease research include exploring new hypotheses regarding disease susceptibility, occurrence and progression, identifying reliable diagnostic, prognostic and therapeutic biomarkers, and translating basic research into appropriate disease-modifying strategies. The most popular view proposes that Parkinson's disease results from the complex interplay between genetic and environmental factors and mechanisms believed to be at work include oxidative stress, mitochondrial dysfunction, excitotoxicity, iron deposition and inflammation. More recently, a plethora of data has accumulated pinpointing an abnormal processing of the neuronal protein alpha-synuclein as a pivotal mechanism leading to aggregation, inclusions formation and degeneration. This protein-oriented scenario logically opens the door to the application of proteomic strategies to this field of research. We here review the current literature on proteomics applied to Parkinson's disease research, with particular emphasis on pathogenesis of sporadic Parkinson's disease in humans. We propose the view that Parkinson's disease may be an acquired or genetically-determined brain proteinopathy involving an abnormal processing of several, rather than individual neuronal proteins, and discuss some pre-analytical and analytical developments in proteomics that may help in verifying this concept.

Tickled PINK1: mitochondrial homeostasis and autophagy in recessive Parkinsonism

Dysregulation of mitochondrial structure and function has emerged as a central factor in the pathogenesis of Parkinson's disease and related parkinsonian disorders (PD). Toxic and environmental injuries and risk factors perturb mitochondrial complex I function, and gene products linked to familial PD often affect mitochondrial biology. Autosomal recessive mutations in PTEN-induced kinase 1 (PINK1) cause an L-DOPA responsive parkinsonian syndrome, stimulating extensive interest in the normal neuroprotective and mitoprotective functions of PINK1. Recent data from mammalian and invertebrate model systems converge upon interactions between PINK1 and parkin, as well as DJ-1, alpha-synuclein and leucine rich repeat kinase 2 (LRRK2). While all studies to date support a neuroprotective role for wild type, but not mutant PINK1, there is less agreement on subcellular compartmentalization of PINK1 kinase function and whether PINK1 promotes mitochondrial fission or fusion. These controversies are reviewed in the context of the dynamic mitochondrial lifecycle, in which mitochondrial structure and function are continuously modulated not only by the fission-fusion machinery, but also by regulation of biogenesis, axonal/dendritic transport and autophagy. A working model is proposed, in which PINK1 loss-of-function results in mitochondrial reactive oxygen species (ROS), cristae/respiratory dysfunction and destabilization of calcium homeostasis, which trigger compensatory fission, autophagy and biosynthetic repair pathways that dramatically alter mitochondrial structure. Concurrent strategies to identify pathways that mediate normal PINK1 function and to identify factors that facilitate appropriate compensatory responses to its loss are both needed to halt the aging-related penetrance and incidence of familial and sporadic PD.

Behavioral and quantitative mitochondrial proteome analyses of the effects of simvastatin: implications for models of neural degeneration

The 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, simvastatin, is used for lowering elevated low-density lipoprotein cholesterol concentrations. This translates into reduced cardiovascular disease-related morbidity and mortality, while the drugs' anti-oxidant and anti-inflammatory properties have earmarked it as a potential treatment strategy against various neurological conditions. Statins have been shown to protect neurons from degeneration in a number of animal models. Although no mechanism completely explains the multiple benefits exerted by statins, emerging evidence suggests that in some degenerative and brain injury models, mitochondrial impairment may play a contributive rate. However, [corrected] evidence lacks to support a directly influencing role for statins on mitochondria-related proteins and motor behavior. Mitochondrial dysfunction may increase oxygen free radical production, which in turn leaves cells susceptible to energy failure, apoptosis and related events [corrected] which could prove fatal. The potential link between simvastatin treatment and mitochondrial function would be supported if key mitochondrial proteins were altered by simvastatin exposure. Using mass spectroscopy (MS), we identified 24 mitochondrial proteins that differed significantly (P < 0.05) in relative abundancy as a result of simvastatin treatment. The identified proteins represented many facets of mitochondrial integrity, with the majority forming part of the electron transport chain machinery, which is necessary for energy production. In a follow-up study, we then addressed whether simvastatin is capable of altering sensorimotor function in a mitochondrial toxin-induced animal model. Rats were pre-treated with simvastatin for 14 days, followed by a single unihemispheric (substantia nigra; SN) injection of rotenone, a mitochondrial complex I (Co-I) inhibitor. Results showed that simvastatin improved motor performance in rotenone-infused rats. The data are consistent with the possibility that alteration of mitochondrial function may contribute to the beneficial effects associated with statin use.

The homocysteine-inducible endoplasmic reticulum stress protein counteracts calcium store depletion and induction of CCAAT enhancer-binding protein homologous protein in a neurotoxin model of Parkinson disease

The endoplasmic reticulum (ER) is a key organelle regulating intracellular Ca(2+) homeostasis. Oxidants and mitochondria-derived free radicals can target ER-based Ca(2+) regulatory proteins and cause uncontrolled Ca(2+) release that may contribute to protracted ER stress and apoptosis. Several ER stress proteins have been suggested to counteract the deregulation of ER Ca(2+) homeostasis and ER stress. Here we showed that knockdown of Herp, an ubiquitin-like domain containing ER stress protein, renders PC12 and MN9D cells vulnerable to 1-methyl-4-phenylpyridinium-induced cytotoxic cell death by a mechanism involving up-regulation of CHOP expression and ER Ca(2+) depletion. Conversely, Herp overexpression confers protection by blocking 1-methyl-4-phenylpyridinium-induced CHOP up-regulation, ER Ca(2+) store depletion, and mitochondrial Ca(2+) accumulation in a manner dependent on a functional ubiquitin-proteasomal protein degradation pathway. Deletion of the ubiquitin-like domain of Herp or treatment with a proteasomal inhibitor abolished the central function of Herp in ER Ca(2+) homeostasis. Thus, elucidating the underlying molecular mechanism(s) whereby Herp counteracts Ca(2+) disturbances will provide insights into the molecular cascade of cell death in dopaminergic neurons and may uncover novel therapeutic strategies to prevent and ameliorate Parkinson disease progression.

Striatal neuroinflammation promotes Parkinsonism in rats

Background

Sporadic Parkinson's disease (PD) is a progressive neurodegenerative disorder with unknown cause, but it has been suggested that neuroinflammation may play a role in pathogenesis of the disease. Neuroinflammatory component in process of PD neurodegeneration was proposed by postmortem, epidemiological and animal model studies. However, it remains unclear how neuroinflammatory factors contribute to dopaminergic neuronal death in PD.

Findings

In this study, we analyzed the relationship among inducible nitric oxide synthase (iNOS)-derived NO, mitochondrial dysfunction and dopaminergic neurodegeneration to examine the possibility that microglial neuroinflammation may induce dopaminergic neuronal loss in the substantia nigra. Unilateral injection of lipopolysaccharide (LPS) into the striatum of rat was followed by immunocytochemical, histological, neurochemical and biochemical analyses. In addition, behavioral assessments including cylinder test and amphetamine-induced rotational behavior test were employed to validate ipsilateral damage to the dopamine nigrostriatal pathway. LPS injection caused progressive degeneration of the dopamine nigrostriatal system, which was accompanied by motor impairments including asymmetric usage of forelimbs and amphetamine-induced turning behavior in animals. Interestingly, some of the remaining nigral dopaminergic neurons had intracytoplasmic accumulation of α-synuclein and ubiquitin. Furthermore, defect in the mitochondrial respiratory chain, and extensive S-nitrosylation/nitration of mitochondrial complex I were detected prior to the dopaminergic neuronal loss. The mitochondrial injury was prevented by treatment with L-N⁶-(l-iminoethyl)-lysine, an iNOS inhibitor, suggesting that iNOS-derived NO is associated with the mitochondrial impairment.

Conclusions

These results implicate neuroinflammation-induced S-nitrosylation/nitration of mitochondrial complex I in mitochondrial malfunction and subsequent degeneration of the nigral dopamine neurons.

Dopamine (DA) induced irreversible proteasome inhibition via DA derived quinones

This study demonstrated that DA and its oxidative metabolites: H2O2 and aminochrome (AM), cyclized DA quinones, could all directly inhibit proteasome activity. DA and AM, especially AM, could induce intensive and irreversible proteasome inhibition, whereas proteasome inhibition induced by H2O2 was weaker and GSH reversible. It was concluded that DA induced irreversible proteasome inhibition via DA-derived quinones, rather than through small molecular weight ROS. The AM was also more toxic than H2O2 to dopaminergic MN9D cells. Furthermore the cytotoxicity and proteasome inhibition induced by DA, AM and H2O2 could be abrogated by GSH, ascorbic acid (AA), Vitamin E, SOD (superoxidase dismutase) or CAT (catalase) with different profiles. Only GSH was potent to abrogate DA, AM or H2O2-induced cell toxicity and proteasome inhibition, as well as to reverse H2O2-induced proteosome inhibition. Therefore, therapeutic strategies to increase GSH level or to use GSH substitutes should function to control PD onset and development.

Evaluation of blastomere biopsy using a mouse model indicates the potential high risk of neurodegenerative disorders in the offspring

Preimplantation genetic diagnosis (PGD), used in clinical practice, is offered to couples that may suffer from a monogenetic disorder, chromosome aneuploidy, or X-linked disease. However, blastomere biopsy, as an indispensable manipulation during the PGD procedure has not been assessed for its long term health implications. Using a mouse model, we investigated the effect of blastomere biopsy of in vitro cultured four-cell embryos on preimplantation development efficiency, postnatal growth, and physiological and behavioral activity compared with control, non-biopsied embryos. The mice generated after blastomere biopsy showed weight increase and some memory decline compared with the control group. Further protein expression profiles in adult brains were analyzed by a proteomics approach. A total of 36 proteins were identified with significant differences between the biopsied and control groups, and the alterations in expression of most of these proteins have been associated with neurodegenerative diseases. Furthermore hypomyelination of the nerve fibers was observed in the brains of mice in the biopsied group. This study suggested that the nervous system may be sensitive to blastomere biopsy procedures and indicated an increased relative risk of neurodegenerative disorders in the offspring generated following blastomere biopsy. Thus, more studies should be performed to address the possible adverse effects of blastomere biopsy on the development of offspring, and the overall safety of PGD technology should be more rigorously assessed.

Why have we failed to achieve neuroprotection in Parkinson's disease?

The development of a neuroprotective therapy that slows, stops, or reverses neurodegeneration in Parkinson's disease (PD) is the single most important unresolved issue in the management of this disorder. Current therapies provide effective control of symptoms, particularly in the early stages of the disease, but disease progression is associated with the development of "nondopaminergic" features such as postural instability, falling, and dementia that are not adequately controlled with existing medications. There are many promising candidate neuroprotective agents based on pathological and laboratory studies, but to date, it has not been possible to determine that any drug has a disease-modifying effect in PD. Obstacles to the development of a neuroprotective therapy in PD include: (1) uncertainty as to the precise cause of cell death in PD and what to target; (2) the lack of an animal model of PD that precisely reflects the etiopathogenesis of the disease, the pattern of dopaminergic and nondopaminergic pathology, and its chronic, progressive nature; (3) determination of the correct dose to use in clinical trials; and (4) delineation of a clinical end point that is an accurate measure of the underlying disease and is not confounded by potential symptomatic effects of a study intervention. New developments in understanding the cause of the disease, in the development of animal models of PD, and in clinical trial methodology will hopefully hasten the resolution of these problems.

Functional models of Parkinson's disease: a valuable tool in the development of novel therapies

Functional models of Parkinson's disease (PD) have led to effective treatment for the motor symptoms. Toxin-based models, such as the 6-hydroxydopamine-lesioned rat and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated primate, have resulted in novel dopaminergic therapies and new therapeutic strategies. They have also been used to study processes underlying motor complications, particularly dyskinesia, and for developing pharmacological approaches to dyskinesia avoidance and suppression. Symptomatic models of PD based on nigrostriatal degeneration have a high degree of predictability of clinical effect of dopaminergic drugs on motor symptoms in humans. However, the effects of nondopaminergic drugs in these models do not translate effectively into clinical efficacy. Newer experimental models of PD have attempted to reproduce the pathogenic process and to involve all areas of the brain pathologically affected in humans. In addition, models showing progressive neuronal death have been sought but so far unsuccessfully. Pathogenic modeling has been attempted using a range of toxins, as well as through the use of transgenic models of gene defects in familial PD and mutant rodent strains. However, there are still no accepted progressive models of PD that mimic the processes known to occur during cell death and that result in the motor deficits, pathology, biochemistry, and drug responsiveness as seen in humans. Nevertheless, functional models of PD have led to many advances in treating the motor symptoms of the disorder, and we have been fortunate to have them available. They are an important reason the treatment of PD is so much better compared with treatments for related illnesses.

A critical evaluation of the ubiquitin-proteasome system in Parkinson's disease

The evidence for impairment in the ubiquitin proteasome system (UPS) in Parkinson's disease (PD) is mounting and becoming increasingly more convincing. However, it is presently unclear whether UPS dysfunction is a cause or result of PD pathology, a crucial distinction which impedes both the understanding of disease pathogenesis and the development of effectual therapeutic approaches. Recent findings discussed within this review offer new insight and provide direction for future research to conclusively resolve this debate.

Neurodegeneration and ageing in the HAART era

Cognitive impairment and neurodegeneration still occur despite highly active antiretroviral therapy (HAART). While there are many potential reasons for this, there is increasing evidence that such impairment occurs in the absence of a clear cause. Furthermore, there are data that some neurodegenerative diseases, especially Alzheimer's or an Alzheimer-like illness, are becoming more common in the context of HAART-treated human immunodeficiency virus (HIV) disease. This review will critically examine the evidence underpinning these observations. Potential mechanisms will be discussed with particular emphasis on the effect of ageing and how it overlaps with the effects of HIV disease itself thereby leading to neurodegeneration. The nature of this overlap will then be explored for its potential role in the facilitated expression and development of neurodegenerative diseases. Lastly, there will be a brief discussion of interventions to minimize such neurodegeneration including optimization of HAART for brain entry.

What causes cell death in Parkinson's disease?

Currently, there is no proven neuroprotective or neurorestorative therapy for Parkinson's disease (PD). Several advances in the genetics of PD have created an opportunity to develop mechanistic-based therapies that hold particular promise for identifying agents that slow and even halt the progression of PD, as well as restore function. Here we review many of the advances in the last decade regarding the identification of new targets for the treatment of PD based on understanding the molecular mechanisms of how mutations in genes linked to PD cause neurodegeneration.

Ubiquitin, the proteasome and protein degradation in neuronal function and dysfunction

Eukaryotic protein degradation by the proteasome and the lysosome is a dynamic and complex process in which ubiquitin has a key regulatory role. The distinctive morphology of the postmitotic neuron creates unique challenges for protein degradation systems with respect to cell-surface protein turnover and substrate delivery to proteolytic machineries that are required for both synaptic plasticity and self-renewal. Moreover, the discovery of ubiquitin-positive protein aggregates in a wide spectrum of neurodegenerative diseases underlines the importance and vulnerability of the degradative system in neurons. In this article, we discuss the molecular mechanism of protein degradation in the neuron with respect to both its function and its dysfunction.

Protein phosphatase 1, protein phosphatase 2A, and calcineurin play a role in estrogen-mediated neuroprotection

It is becoming increasingly clear that protein phosphatases are important modulators of cellular function and that disruption of these proteins are involved in neurodegenerative disease processes. Serine/threonine protein phosphatases (PP) such as protein phosphatase PP1, PP2A, and calcineurin are involved in hyperphosphorylation of tau- as well as beta-amyloid-induced cell death. We have previously shown serine/threonine protein phosphatases to be involved in estrogen-mediated neuroprotection. The purpose of this study was to delineate the role of PP1, PP2A, and calcineurin in the mechanism of estrogen mediated neuroprotection against oxidative stress and excitotoxicity. Treatment with protein phosphatases inhibitor II, endothall, or cyclosporin A, which are specific inhibitors of PP1, PP2A, and calcineurin, respectively, did not have an effect on cell viability. However, in combination, these inhibitors adversely affected cell survival, which suggests the importance of serine/threonine protein phosphatases in maintenance of cellular function. Inhibitors of PP1, PP2A, and calcineurin attenuated the protective effects of estrogen against glutamate-induced -neurotoxicity but did not completely abrogate the estrogen-mediated protection. The attenuation of estrogen-induced neuroprotection was achieved through decrease in the activity of theses serine/threonine phosphatases without the concomitant decrease in protein expression. In an animal model, transient middle cerebral artery occlusion caused a 50% decrease in levels of PP1, PP2A, and PP2B ipsilateral to the lesion in a manner that was prevented by estradiol pretreatment. Therefore, we conclude that in the face of cytotoxic challenges in vitro and in vivo, estrogens maintain the function of PP1, PP2A, and calcineurin.