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Find video protocols related to scientific articles indexed in Pubmed.
Intranasal delivery of bone marrow derived mesenchymal stem cells, macrophages, and microglia to the brain in mouse models of Alzheimer?s and Parkinson?s disease.
Cell Transplant
PUBLISHED: 10-09-2014
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In view of the rapid preclinical development of cell-based therapies for neurodegenerative disorders, traumatic brain injury, and tumors, the safe and efficient delivery and targeting of therapeutic cells to the central nervous system is critical for maintaining therapeutic efficacy and safety in the respective disease models. Our previous data demonstrated therapeutically efficacious and targeted delivery of mesenchymal stem cells (MSCs) to the brain in the rat 6-hydroxydopamine model of Parkinson?s disease (PD). The present study examined delivery of bone marrow derived MSCs, macrophages, and microglia to the brain in a transgenic model of PD ((Thy1)-h[A30P] ?S) and an APP/PS1 model of Alzheimer?s disease (AD) via intranasal application (INA). INA of microglia in na?ve BL/6 mice led to targeted and effective delivery of cells to the brain. Quantitative PCR analysis of eGFP DNA showed that the brain contained the highest amount of eGFP-microglia (up to 2.1x10(4)) after INA of 1x10(6) cells, while the total amount of cells detected in peripheral organs did not exceed 3.4x10(3). Seven days after INA, MSCs expressing eGFP were detected in the olfactory bulb (OB), cortex, amygdala, striatum, hippocampus, cerebellum, and brainstem of (Thy1)-h[A30P] ?S transgenic mice, showing predominant distribution within the OB and brainstem. INA of eGFP-expressing macrophages in 13 month-old APP/PS1 mice led to delivery of cells to the OB, hippocampus, cortex, and cerebellum. Both, MSCs and macrophages contained Iba-1-positive population of small microglia-like cells and Iba-1-negative large rounded cells showing either intracellular Amyloid beta (macrophages in APP/PS1 model) or ?-Synuclein (MSCs in (Thy1)-h[A30P] ?S model) immunoreactivity. Here we show, for the first time, intranasal delivery of cells to the brain of transgenic PD and AD mouse models. Additional work is needed to determine the optimal dosage (single treatment regimen or repeated administrations) to achieve functional improvement in these mouse models with intranasal microglia/macrophages and MSCs. This manuscript is published as part of the International Association of Neurorestoratology (IANR) special issue of Cell Transplantation.
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Regulatory effects of SKAR in interferon ? signaling and its role in the generation of type I IFN responses.
Proc. Natl. Acad. Sci. U.S.A.
PUBLISHED: 07-21-2014
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We provide evidence that S6 kinase 1 (S6K1) Aly/REF-like target (SKAR) is engaged in IFN-? signaling and plays a key role in the generation of IFN responses. Our data demonstrate that IFN-? induces phosphorylation of SKAR, which is mediated by either the p90 ribosomal protein S6 kinase (RSK) or p70 S6 kinase (S6K1), in a cell type-specific manner. This type I IFN-inducible phosphorylation of SKAR results in enhanced interaction with the eukaryotic initiation factor (eIF)4G and recruitment of activated RSK1 to 5' cap mRNA. Our studies also establish that SKAR is present in cap-binding CBP80 immune complexes and that this interaction is mediated by eIF4G. We demonstrate that inducible protein expression of key IFN-?-regulated protein products such as ISG15 and p21(WAF1/CIP1) requires SKAR activity. Importantly, our studies define a requirement for SKAR in the generation of IFN-?-dependent inhibitory effects on malignant hematopoietic progenitors from patients with chronic myeloid leukemia or myeloproliferative neoplasms. Taken altogether, these findings establish critical and essential roles for SKAR in the regulation of mRNA translation of IFN-sensitive genes and induction of IFN-? biological responses.
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The ubiquitin-conjugating enzymes UBE2N, UBE2L3 and UBE2D2/3 are essential for Parkin-dependent mitophagy.
J. Cell. Sci.
PUBLISHED: 06-06-2014
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Depolarized mitochondria are degraded by mitophagy in a process that depends on the Parkinson's disease gene products PINK1 and Parkin. This is accompanied by ubiquitylation of several mitochondrial substrates. The roles of E2 ubiquitin-conjugating enzymes (UBE2) in mitophagy are poorly understood. Here, we investigate a set of UBE2 enzymes that might regulate Parkin-mediated mitophagy. Knockdown of the E2 enzymes UBE2N, UBE2L3 or UBE2D2 and UBE2D3 (UBE2D2/3) significantly reduced autophagic clearance of depolarized mitochondria. However, this did not interfere with mitochondrial PINK1 stabilization and Parkin translocation. UBE2N knockdown prevented specifically K63-linked ubiquitylation at mitochondrial sites. Nevertheless, polyubiquitin and p62 (officially known as SQSTM1) were still found on mitochondria after individual UBE2 knockdown. Knockdown of all of these UBE2s together significantly reduced mitochondrial polyubiquitylation and p62 recruitment. Moreover, reduced ubiquitylation of mitofusins, the mitochondrial import receptor subunits TOM20 and TOM70, the voltage-dependent anion channel protein 1 and Parkin was observed in cells silenced for all of these UBE2s. A version of Parkin with a mutation in the active site (C431S) failed to ubiquitylate these mitochondrial substrates even in the presence of UBE2s. We conclude that UBE2N, UBE2L3 and UBE2D2/3 synergistically contribute to Parkin-mediated mitophagy.
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Diet-induced obesity accelerates the onset of terminal phenotypes in ?-synuclein transgenic mice.
J. Neurochem.
PUBLISHED: 05-23-2014
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Parkinson's disease (PD) and diabetes belong to the most common neurodegenerative and metabolic syndromes, respectively. Epidemiological links between these two frequent disorders are controversial. The neuropathological hallmarks of PD are protein aggregates composed of amyloid-like fibrillar and serine-129 phosphorylated (pS129) ?-synuclein (AS). To study if diet-induced obesity could be an environmental risk factor for PD-related ?-synucleinopathy, transgenic (TG) mice, expressing the human mutant A30P AS in brain neurons, were subjected after weaning to a lifelong high fat diet (HFD). The TG mice became obese and glucose-intolerant, as did the wild-type controls. Upon aging, HFD significantly accelerated the onset of the lethal locomotor phenotype. Coinciding with the premature movement phenotype and death, HFD accelerated the age of onset of brainstem ?-synucleinopathy as detected by immunostaining with antibodies against pathology-associated pS129. Amyloid-like neuropathology was confirmed by thioflavin S staining. Accelerated onset of neurodegeneration was indicated by Gallyas silver-positive neuronal dystrophy as well as astrogliosis. Phosphorylation of the activation sites of the pro-survival signaling intermediate Akt was reduced in younger TG mice after HFD. Thus, diet-induced obesity may be an environmental risk factor for the development of ?-synucleinopathies. The molecular and cellular mechanisms remain to be further elucidated. Life-long high fat diet (HFD) induces obesity and glucose intolerance in a transgenic mouse model for ?-synucleinopathy and thereby leads to decreased life span as well as accelerated age of onset of the terminal phenotype. This is accompanied by increased neuroinflammation and premature ?-synuclein pathology in the brainstems of the HFD-fed mice.
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UBE2E ubiquitin-conjugating enzymes and ubiquitin isopeptidase Y regulate TDP-43 protein ubiquitination.
J. Biol. Chem.
PUBLISHED: 05-13-2014
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Trans-activation element DNA-binding protein of 43 kDa (TDP-43) characterizes insoluble protein aggregates in distinct subtypes of frontotemporal lobar degeneration and amyotrophic lateral sclerosis. TDP-43 mediates many RNA processing steps within distinct protein complexes. Here we identify novel TDP-43 protein interactors found in a yeast two-hybrid screen using an adult human brain cDNA library. We confirmed the TDP-43 interaction of seven hits by co-immunoprecipitation and assessed their co-localization in HEK293E cells. As pathological TDP-43 is ubiquitinated, we focused on the ubiquitin-conjugating enzyme UBE2E3 and the ubiquitin isopeptidase Y (UBPY). When cells were treated with proteasome inhibitor, ubiquitinated and insoluble TDP-43 species accumulated. All three UBE2E family members could enhance the ubiquitination of TDP-43, whereas catalytically inactive UBE2E3(C145S) was much less efficient. Conversely, silencing of UBE2E3 reduced TDP-43 ubiquitination. We examined 15 of the 48 known disease-associated TDP-43 mutants and found that one was excessively ubiquitinated. This strong TDP-43(K263E) ubiquitination was further enhanced by proteasomal inhibition as well as UBE2E3 expression. Conversely, UBE2E3 silencing and expression of UBPY reduced TDP-43(K263E) ubiquitination. Moreover, wild-type but not active site mutant UBPY reduced ubiquitination of TDP-43 C-terminal fragments and of a nuclear import-impaired mutant. In Drosophila melanogaster, UBPY silencing enhanced neurodegenerative TDP-43 phenotypes and the accumulation of insoluble high molecular weight TDP-43 and ubiquitin species. Thus, UBE2E3 and UBPY participate in the regulation of TDP-43 ubiquitination, solubility, and neurodegeneration.
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Immunotherapy targeting ?-synuclein protofibrils reduced pathology in (Thy-1)-h[A30P] ?-synuclein mice.
Neurobiol. Dis.
PUBLISHED: 03-25-2014
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Several lines of evidence suggest that accumulation of aggregated alpha-synuclein (?-synuclein) in the central nervous system (CNS) is an early pathogenic event in Parkinson's disease and other Lewy body disorders. In recent years, animal studies have indicated immunotherapy with antibodies directed against ?-synuclein as a promising novel treatment strategy. Since large ?-synuclein oligomers, or protofibrils, have been demonstrated to possess pronounced cytotoxic properties, such species should be particularly attractive as therapeutic targets. In support of this, (Thy-1)-h[A30P] ?-synuclein transgenic mice with motor dysfunction symptoms were found to display increased levels of ?-synuclein protofibrils in the CNS. An ?-synuclein protofibril-selective monoclonal antibody (mAb47) was evaluated in this ?-synuclein transgenic mouse model. As measured by ELISA, 14month old mice treated for 14weeks with weekly intraperitoneal injections of mAb47 displayed significantly lower levels of both soluble and membrane-associated protofibrils in the spinal cord. Besides the lower levels of pathogenic ?-synuclein demonstrated, a reduction of motor dysfunction in transgenic mice upon peripheral administration of mAb47 was indicated. Thus, immunotherapy with antibodies targeting toxic ?-synuclein species holds promise as a future disease-modifying treatment in Parkinson's disease and related disorders.
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Overexpression of the calpain-specific inhibitor calpastatin reduces human alpha-Synuclein processing, aggregation and synaptic impairment in [A30P]?Syn transgenic mice.
Hum. Mol. Genet.
PUBLISHED: 03-11-2014
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Lewy bodies, a pathological hallmark of Parkinson's disease (PD), contain aggregated alpha-synuclein (?Syn), which is found in several modified forms and can be discovered phosphorylated, ubiquitinated and truncated. Aggregation-prone truncated species of ?Syn caused by aberrant cleavage of this fibrillogenic protein are hypothesized to participate in its sequestration into inclusions subsequently leading to synaptic dysfunction and neuronal death. Here, we investigated the role of calpain cleavage of ?Syn in vivo by generating two opposing mouse models. We crossed into human [A30P]?Syn transgenic (i) mice deficient for calpastatin, a calpain-specific inhibitor, thus enhancing calpain activity (SynCAST(-)) and (ii) mice overexpressing human calpastatin leading to reduced calpain activity (SynCAST(+)). As anticipated, a reduced calpain activity led to a decreased number of ?Syn-positive aggregates, whereas loss of calpastatin led to increased truncation of ?Syn in SynCAST(-). Furthermore, overexpression of calpastatin decreased astrogliosis and the calpain-dependent degradation of synaptic proteins, potentially ameliorating the observed neuropathology in [A30P]?Syn and SynCAST(+) mice. Overall, our data further support a crucial role of calpains, particularly of calpain 1, in the pathogenesis of PD and in disease-associated aggregation of ?Syn, indicating a therapeutic potential of calpain inhibition in PD.
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Interferon-? induces leucine-rich repeat kinase LRRK2 via extracellular signal-regulated kinase ERK5 in macrophages.
J. Neurochem.
PUBLISHED: 01-17-2014
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The gene encoding leucine-rich repeat kinase 2 (LRRK2) comprises a major risk factor for Parkinson's disease. Recently, it has emerged that LRRK2 plays important roles in the immune system. LRRK2 is induced by interferon-? (IFN-?) in monocytes, but the signaling pathway is not known. Here, we show that IFN-?-mediated induction of LRRK2 was suppressed by pharmacological inhibition and RNA interference of the extracellular signal-regulated kinase 5 (ERK5). This was confirmed by LRRK2 immunostaining, which also revealed that the morphological responses to IFN-? were suppressed by ERK5 inhibitor treatment. Both human acute monocytic leukemia THP-1 cells and human peripheral blood monocytes stimulated the ERK5-LRRK2 pathway after differentiation into macrophages. Thus, LRRK2 is induced via a novel, ERK5-dependent IFN-? signal transduction pathway, pointing to new functions of ERK5 and LRRK2 in human macrophages. Leucine-rich repeat kinase 2 (LRRK2) is a major risk factor for the development of Parkinson's disease (PD). However, the role of LRRK2 in the affected neurons remains enigmatic. Recently, LRRK2 has been reported to be strongly expressed in the immune system. Here, we demonstrate that LRRK2 is induced by Interferon gamma via extracellular signal-regulated kinase 5 (ERK5) in macrophages, thus providing new insights in LRRK2 and ERK5 biology.
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Overexpression of synphilin-1 promotes clearance of soluble and misfolded alpha-synuclein without restoring the motor phenotype in aged A30P transgenic mice.
Hum. Mol. Genet.
PUBLISHED: 09-24-2013
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Lewy bodies and neurites are the pathological hallmark of Parkinsons disease. These structures are composed of fibrillized and ubiquitinated alpha-synuclein suggesting that impaired protein clearance is an important event in aggregate formation. The A30P mutation is known for its fast oligomerization, but slow fibrillization rate. Despite its toxicity to neurons, mechanisms involved in either clearance or conversion of A30P alpha-synuclein from its soluble state into insoluble fibrils and their effects in vivo are poorly understood. Synphilin-1 is present in Lewy bodies, interacting with alpha-synuclein in vivo and in vitro and promotes its sequestration into aggresomes, which are thought to act as cytoprotective agents facilitating protein degradation. We therefore crossed animals overexpressing A30P alpha-synuclein with synphilin-1 transgenic mice to analyze its impact on aggregation, protein clearance and phenotype progression. We observed that co-expression of synphilin-1 mildly delayed the motor phenotype caused by A30P alpha-synuclein. Additionally, the presence of N- and C-terminal truncated alpha-synuclein species and fibrils were strongly reduced in double-transgenic mice when compared with single-transgenic A30P mice. Insolubility of mutant A30P and formation of aggresomes was still detectable in aged double-transgenic mice, paralleled by an increase of ubiquitinated proteins and high autophagic activity. Hence, this study supports the notion that co-expression of synphilin-1 promotes formation of autophagic-susceptible aggresomes and consecutively the degradation of human A30P alpha-synuclein. Notably, although synphilin-1 overexpression significantly reduced formation of fibrils and astrogliosis in aged animals, a similar phenotype is present in single- and double-transgenic mice suggesting additional neurotoxic processes in disease progression.
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Off-pathway ?-synuclein oligomers seem to alter ?-synuclein turnover in a cell model but lack seeding capability in vivo.
Amyloid
PUBLISHED: 09-20-2013
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Aggregated ?-synuclein is the major component of Lewy bodies, protein inclusions observed in the brain in neurodegenerative disorders such as Parkinsons disease and dementia with Lewy bodies. Experimental evidence indicates that ?-synuclein potentially can be transferred between cells and act as a seed to accelerate the aggregation process. Here, we investigated in vitro and in vivo seeding effects of ?-synuclein oligomers induced by the reactive aldehyde 4-oxo-2-nonenal (ONE). As measured by a Thioflavin-T based fibrillization assay, there was an earlier onset of aggregation when ?-synuclein oligomers were added to monomeric ?-synuclein. In contrast, exogenously added ?-synuclein oligomers did not induce aggregation in a cell model. However, cells overexpressing ?-synuclein that were treated with the oligomers displayed reduced ?-synuclein levels, indicating that internalized oligomers either decreased the expression or accelerated the degradation of transfected ?-synuclein. Also in vivo there were no clear seeding effects, as intracerebral injections of ?-synuclein oligomers into the neocortex of ?-synuclein transgenic mice did not induce formation of proteinase K resistant ?-synuclein pathology. Taken together, we could observe a seeding effect of the ONE-induced ?-synuclein oligomers in a fibrillization assay, but neither in a cell nor in a mouse model.
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Parkinsons disease: dopaminergic nerve cell model is consistent with experimental finding of increased extracellular transport of alpha-synuclein.
BMC Neurosci
PUBLISHED: 02-26-2013
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Parkinsons disease is an age-related disease whose pathogenesis is not completely known. Animal models exist for investigating the disease but not all results can be easily transferred to humans. Therefore, mathematical or probabilistic models for the human disease are to be constructed extit{in silico} in order to predict specific processes within a cell, such as the dopamine metabolism and transport processes in a neuron.
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FAS-dependent cell death in ?-synuclein transgenic oligodendrocyte models of multiple system atrophy.
PLoS ONE
PUBLISHED: 01-25-2013
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Multiple system atrophy is a parkinsonian neurodegenerative disorder. It is cytopathologically characterized by accumulation of the protein p25? in cell bodies of oligodendrocytes followed by accumulation of aggregated ?-synuclein in so-called glial cytoplasmic inclusions. p25? is a stimulator of ?-synuclein aggregation, and coexpression of ?-synuclein and p25? in the oligodendroglial OLN-t40-AS cell line causes ?-synuclein aggregate-dependent toxicity. In this study, we investigated whether the FAS system is involved in ?-synuclein aggregate dependent degeneration in oligodendrocytes and may play a role in multiple system atrophy. Using rat oligodendroglial OLN-t40-AS cells we demonstrate that the cytotoxicity caused by coexpressing ?-synuclein and p25? relies on stimulation of the death domain receptor FAS and caspase-8 activation. Using primary oligodendrocytes derived from PLP-?-synuclein transgenic mice we demonstrate that they exist in a sensitized state expressing pro-apoptotic FAS receptor, which makes them sensitive to FAS ligand-mediated apoptosis. Immunoblot analysis shows an increase in FAS in brain extracts from multiple system atrophy cases. Immunohistochemical analysis demonstrated enhanced FAS expression in multiple system atrophy brains notably in oligodendrocytes harboring the earliest stages of glial cytoplasmic inclusion formation. Oligodendroglial FAS expression is an early hallmark of oligodendroglial pathology in multiple system atrophy that mechanistically may be coupled to ?-synuclein dependent degeneration and thus represent a potential target for protective intervention.
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Monoclonal antibodies selective for ?-synuclein oligomers/protofibrils recognize brain pathology in Lewy body disorders and ?-synuclein transgenic mice with the disease-causing A30P mutation.
J. Neurochem.
PUBLISHED: 01-21-2013
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Inclusions of intraneuronal alpha-synuclein (?-synuclein) can be detected in brains of patients with Parkinsons disease and dementia with Lewy bodies. The aggregation of ?-synuclein is a central feature of the disease pathogenesis. Among the different ?-synuclein species, large oligomers/protofibrils have particular neurotoxic properties and should therefore be suitable as both therapeutic and diagnostic targets. Two monoclonal antibodies, mAb38F and mAb38E2, with high affinity and strong selectivity for large ?-synuclein oligomers were generated. These antibodies, which do not bind amyloid-beta or tau, recognize Lewy body pathology in brains from patients with Parkinsons disease and dementia with Lewy bodies and detect pathology earlier in ?-synuclein transgenic mice than linear epitope antibodies. An oligomer-selective sandwich ELISA, based on mAb38F, was set up to analyze brain extracts of the transgenic mice. The overall levels of ?-synuclein oligomers/protofibrils were found to increase with age in these mice, although the levels displayed a large interindividual variation. Upon subcellular fractionation, higher levels of ?-synuclein oligomers/protofibrils could be detected in the endoplasmic reticulum around the age when behavioral disturbances develop. In summary, our novel oligomer-selective ?-synuclein antibodies recognize relevant pathology and should be important tools to further explore the pathogenic mechanisms in Lewy body disorders. Moreover, they could be potential candidates both for immunotherapy and as reagents in an assay to assess a potential disease biomarker.
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Regulation of PINK1-Parkin-mediated mitophagy.
Autophagy
PUBLISHED: 12-29-2011
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Parkinson disease (PD) is a devastating disorder of the nervous system for which no cure exists. Although the exact mechanisms involved in the pathogenesis of PD are unclear, very recently, a novel cellular process has been identified that promises great future potential. Two PD-associated genes have been found to converge on the emerging mitophagy pathway that links the two major cellular dysfunctions implicated in the pathogenesis of PD. Thereby, PINK1 and Parkin physically associate and functionally cooperate to identify and label damaged mitochondria for selective degradation via autophagy. PD-associated mutations in both genes disrupt mitophagy although through different mechanisms, revealing a sequential multistep process. Further key players that tie into this process have been identified and provide the framework for future research aiming at a complete dissection of this neuroprotective pathway. This may not only yield novel targets for therapeutic intervention in PD, but possibly for other neurodegenerative disorders as well.
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TDP-43 regulates global translational yield by splicing of exon junction complex component SKAR.
Nucleic Acids Res.
PUBLISHED: 11-25-2011
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TDP-43 is linked to neurodegenerative diseases including frontotemporal dementia and amyotrophic lateral sclerosis. Mostly localized in the nucleus, TDP-43 acts in conjunction with other ribonucleoproteins as a splicing co-factor. Several RNA targets of TDP-43 have been identified so far, but its role(s) in pathogenesis remains unclear. Using Affymetrix exon arrays, we have screened for the first time for splicing events upon TDP-43 knockdown. We found alternative splicing of the ribosomal S6 kinase 1 (S6K1) Aly/REF-like target (SKAR) upon TDP-43 knockdown in non-neuronal and neuronal cell lines. Alternative SKAR splicing depended on the first RNA recognition motif (RRM1) of TDP-43 and on 5-GA-3 and 5-UG-3 repeats within the SKAR pre-mRNA. SKAR is a component of the exon junction complex, which recruits S6K1, thereby facilitating the pioneer round of translation and promoting cell growth. Indeed, we found that expression of the alternatively spliced SKAR enhanced S6K1-dependent signaling pathways and the translational yield of a splice-dependent reporter. Consistent with this, TDP-43 knockdown also increased translational yield and significantly increased cell size. This indicates a novel mechanism of deregulated translational control upon TDP-43 deficiency, which might contribute to pathogenesis of the protein aggregation diseases frontotemporal dementia and amyotrophic lateral sclerosis.
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TDP-43 knockdown impairs neurite outgrowth dependent on its target histone deacetylase 6.
Mol Neurodegener
PUBLISHED: 08-30-2011
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Trans-activation response element (TAR) DNA binding protein of 43kDa (TDP-43) is causally related to the neurodegenerative diseases frontotemporal dementia and amyotrophic lateral sclerosis being the hallmark protein in the disease-characteristic neuropathological lesions and via genetic linkage. Histone deacetylase 6 (HDAC6) is an established target of the RNA-binding protein TDP-43. HDAC6 is an unusual cytosolic deacetylase enzyme, central for a variety of pivotal cellular functions including aggregating protein turnover, microtubular dynamics and filopodia formation. All these functions are important in the context of neurodegenerative proteinopathies involving TDP-43. We have previously shown in a human embryonic kidney cell line that TDP-43 knockdown significantly impairs the removal of a toxic, aggregating polyQ ataxin-3 fusion protein in an HDAC6-dependent manner. Here we investigated the influence of TDP-43 and its target HDAC6 on neurite outgrowth.
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TDP-43 and FUS/TLS: cellular functions and implications for neurodegeneration.
FEBS J.
PUBLISHED: 08-24-2011
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TDP-43 (transactive response binding protein of 43 kDa) and FUS (fused in sarcoma) comprise the neuropathological protein aggregates of distinct subtypes of the neurodegenerative diseases frontotemporal lobar degeneration and amyotrophic lateral sclerosis. Moreover, the genes encoding TDP-43 and FUS are linked to these diseases. Both TDP-43 and FUS contain RNA binding motifs, and specific targets are being identified. Potential actions of TDP-43 and FUS include transcriptional regulation, mRNA processing and micro RNA biogenesis. These activities are probably modulated by interacting proteins in cell type specific manners as well as distinctly within the nucleus and cytosol, as both proteins shuttle between these compartments. In this minireview the specific functions of TDP-43 and FUS are described and discussed in the context of how TDP-43 and FUS may contribute to the pathogenesis of frontotemporal lobar degeneration and amyotrophic lateral sclerosis.
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Neuropathology in mice expressing mouse alpha-synuclein.
PLoS ONE
PUBLISHED: 06-15-2011
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?-Synuclein (?SN) in human is tightly linked both neuropathologically and genetically to Parkinsons disease (PD) and related disorders. Disease-causing properties in vivo of the wildtype mouse ortholog (m?SN), which carries a threonine at position 53 like the A53T human mutant version that is genetically linked to PD, were never reported. To this end we generated mouse lines that express m?SN in central neurons at levels reaching up to six-fold compared to endogenous m?SN. Unlike transgenic mice expressing human wildtype or mutant forms of ?SN, these m?SN transgenic mice showed pronounced ubiquitin immunopathology in spinal cord and brainstem. Isoelectric separation of m?SN species revealed multiple isoforms including two Ser129-phosphorylated species in the most severely affected brain regions. Neuronal Ser129-phosphorylated ?SN occurred in granular and small fibrillar aggregates and pathological staining patterns in neurites occasionally revealed a striking ladder of small alternating segments staining either for Ser129-phosphorylated ?SN or ubiquitin but not both. Axonal degeneration in long white matter tracts of the spinal cord, with breakdown of myelin sheaths and degeneration of neuromuscular junctions with loss of integrity of the presynaptic neurofilament network in m?SN transgenic mice, was similar to what we have reported for mice expressing human ?SN wildtype or mutant forms. In hippocampal neurons, the m?SN protein accumulated and was phosphorylated but these neurons showed no ubiquitin immunopathology. In contrast to the early-onset motor abnormalities and muscle weakness observed in mice expressing human ?SN, m?SN transgenic mice displayed only end-stage phenotypic alterations that manifested alongside with neuropathology. Altogether these findings show that increased levels of wildtype m?SN does not induce early-onset behavior changes, but drives end-stage pathophysiological changes in murine neurons that are strikingly similar to those evoked by expression of human wildtype or mutant forms.
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Olfactory neuron-specific expression of A30P ?-synuclein exacerbates dopamine deficiency and hyperactivity in a novel conditional model of early Parkinsons disease stages.
Neurobiol. Dis.
PUBLISHED: 04-18-2011
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Mutations in the N-terminus of the gene encoding ?-synuclein (?-syn) are linked to autosomal dominantly inherited Parkinsons disease (PD). The vast majority of PD patients develop neuropsychiatric symptoms preceding motor impairments. During this premotor stage, synucleinopathy is first detectable in the olfactory bulb (OB) and brain stem nuclei; however its impact on interconnected brain regions and related symptoms is still less far understood. Using a novel conditional transgenic mouse model, displaying region-specific expression of human mutant ?-syn, we evaluated effect and reversibility of olfactory synucleinopathy. Our data showed that induction of mutant A30P ?-syn expression increased transgenic deposition into somatodendritic compartment of dopaminergic neurons, without generating fibrillar inclusions. We found reversibly reduced levels of dopamine and metabolites in the OB, suggesting an impact of A30P ?-syn on olfactory neurotransmitter content. We further showed that mutant A30P expression led to neurodegenerative changes on an ultrastructural level and a behaviorally hyperactive response correlated with novelty, odor processing and stress associated with an increased dopaminergic tone in midbrain regions. Our present data indicate that mutant (A30P) ?-syn is directly implicated in reduction of dopamine signaling in OB interneurons, which mediates further alterations in brain regions without transgenic expression leading functionally to a hyperactive response. These modulations of neurotransmission may underlie in part some of the early neuropsychiatric symptoms in PD preceding dysfunction of the nigrostriatal dopaminergic system.
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Novel regulation of parkin function through c-Abl-mediated tyrosine phosphorylation: implications for Parkinsons disease.
J. Neurosci.
PUBLISHED: 01-07-2011
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Mutations in parkin, an E3 ubiquitin ligase, are the most common cause of autosomal-recessive Parkinsons disease (PD). Here, we show that the stress-signaling non-receptor tyrosine kinase c-Abl links parkin to sporadic forms of PD via tyrosine phosphorylation. Under oxidative and dopaminergic stress, c-Abl was activated in cultured neuronal cells and in striatum of adult C57BL/6 mice. Activated c-Abl was found in the striatum of PD patients. Concomitantly, parkin was tyrosine-phosphorylated, causing loss of its ubiquitin ligase and cytoprotective activities, and the accumulation of parkin substrates, AIMP2 (aminoacyl tRNA synthetase complex-interacting multifunctional protein 2) (p38/JTV-1) and FBP-1.STI-571, a selective c-Abl inhibitor, prevented tyrosine phosphorylation of parkin and restored its E3 ligase activity and cytoprotective function both in vitro and in vivo. Our results suggest that tyrosine phosphorylation of parkin by c-Abl is a major post-translational modification that leads to loss of parkin function and disease progression in sporadic PD. Moreover, inhibition of c-Abl offers new therapeutic opportunities for blocking PD progression.
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The PINK1/Parkin-mediated mitophagy is compromised by PD-associated mutations.
Autophagy
PUBLISHED: 10-03-2010
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Mitochondrial dysfunction is an early sign of many neurodegenerative diseases. Very recently, two Parkinson disease (PD) associated genes, PINK1 and Parkin, were shown to mediate the degradation of damaged mitochondria via selective autophagy (mitophagy). PINK1 kinase activity is needed for prompt and efficient Parkin recruitment to impaired mitochondria. PD-associated Parkin mutations interfere with the process of mitophagy at distinct steps. Here we show that whole mitochondria are turned over via macroautophagy. Moreover, disease-associated PINK1 mutations also compromise the selective degradation of depolarized mitochondria. This may be due to the decreased physical binding activity of PD-linked PINK1 mutations to Parkin. Thus, PINK1 mutations abrogate autophagy of impaired mitochondria upstream of Parkin. In addition to compromised PINK1 kinase activity, reduced binding of PINK1 to Parkin leads to failure in Parkin mitochondrial translocation, resulting in the accumulation of damaged mitochondria, which may contribute to disease pathogenesis.
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Over-expression of alpha-synuclein in the nervous system enhances axonal degeneration after peripheral nerve lesion in a transgenic mouse strain.
J. Neurochem.
PUBLISHED: 05-26-2010
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Wallerian degeneration in peripheral nerves occurs after a traumatic insult when the distal nerve part degenerates while peripheral macrophages enter the nerve stump and remove the accruing debris by phagozytosis. We used an experimental model to investigate the effect of either the absence or over-expression of alpha-synuclein (alpha-syn) after transecting the sciatic nerves of mice. alpha-Synuclein is a major component of Lewy bodies and its aggregation results in a premature destruction of nerve cells. It has also been found present in different peripheral nerves but its role in the axon remains still unclear. Following sciatic nerve transection in different mouse strains, we investigated the numbers of invading macrophages, the amounts of remaining myelin and axons 6 days after injury. All mice showed clear signs of Wallerian degeneration, but transgenic mice expressing human wild-type alpha-syn showed lower numbers of invading macrophages, less preserved myelin and significantly lower numbers of preserved axons in comparison with either knockout mice or a mouse strain with a spontaneous deletion of alpha-syn. The use of protein aggregation filtration blots and paraffin-embedded tissue blots displayed depositions of alpha-syn aggregates within sciatic nerve axons of transgenic mice. Thicker myelin sheaths and higher numbers of mitochondria were detected in old alpha-syn transgenic mice. In a human sural nerve, alpha-syn could also be identified within axons. Thus, alpha-syn and its aggregates are not only a component of Lewy bodies and synapses but also of axons and these aggregates might interfere with axonal transport. alpha-Synuclein transgenic mice represent an appropriate model for investigations on axonal transport in neurodegenerative diseases.
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TDP-43-mediated neuron loss in vivo requires RNA-binding activity.
PLoS ONE
PUBLISHED: 05-07-2010
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Alteration and/or mutations of the ribonucleoprotein TDP-43 have been firmly linked to human neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). The relative impacts of TDP-43 alteration, mutation, or inherent protein function on neural integrity, however, remain less clear--a situation confounded by conflicting reports based on transient and/or random-insertion transgenic expression. We therefore performed a stringent comparative investigation of impacts of these TDP-43 modifications on neural integrity in vivo. To achieve this, we systematically screened ALS/FTLD-associated and synthetic TDP-43 isoforms via same-site gene insertion and neural expression in Drosophila; followed by transposon-based motor neuron-specific transgenesis in a chick vertebrate system. Using this bi-systemic approach we uncovered a requirement of inherent TDP-43 RNA-binding function--but not ALS/FTLD-linked mutation, mislocalization, or truncation--for TDP-43-mediated neurotoxicity in vivo.
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Reduced basal autophagy and impaired mitochondrial dynamics due to loss of Parkinsons disease-associated protein DJ-1.
PLoS ONE
PUBLISHED: 01-27-2010
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Mitochondrial dysfunction and degradation takes a central role in current paradigms of neurodegeneration in Parkinsons disease (PD). Loss of DJ-1 function is a rare cause of familial PD. Although a critical role of DJ-1 in oxidative stress response and mitochondrial function has been recognized, the effects on mitochondrial dynamics and downstream consequences remain to be determined.
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PINK1/Parkin-mediated mitophagy is dependent on VDAC1 and p62/SQSTM1.
Nat. Cell Biol.
PUBLISHED: 01-24-2010
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Parkinsons disease is the most common neurodegenerative movement disorder. Mutations in PINK1 and PARKIN are the most frequent causes of recessive Parkinsons disease. However, their molecular contribution to pathogenesis remains unclear. Here, we reveal important mechanistic steps of a PINK1/Parkin-directed pathway linking mitochondrial damage, ubiquitylation and autophagy in non-neuronal and neuronal cells. PINK1 kinase activity and its mitochondrial localization sequence are prerequisites to induce translocation of the E3 ligase Parkin to depolarized mitochondria. Subsequently, Parkin mediates the formation of two distinct poly-ubiquitin chains, linked through Lys 63 and Lys 27. In addition, the autophagic adaptor p62/SQSTM1 is recruited to mitochondrial clusters and is essential for the clearance of mitochondria. Strikingly, we identified VDAC1 (voltage-dependent anion channel 1) as a target for Parkin-mediated Lys 27 poly-ubiquitylation and mitophagy. Moreover, pathogenic Parkin mutations interfere with distinct steps of mitochondrial translocation, ubiquitylation and/or final clearance through mitophagy. Thus, our data provide functional links between PINK1, Parkin and the selective autophagy of mitochondria, which is implicated in the pathogenesis of Parkinsons disease.
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Parkinsons disease-associated DJ-1 modulates innate immunity signaling in Caenorhabditis elegans.
J Neural Transm
PUBLISHED: 01-12-2010
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DJ-1 is a neuroprotective gene mutated in recessive Parkinsons disease (PD). In addition to direct protective functions in neurons, DJ-1 regulates neuroinflammatory signaling in primary mouse brain astrocytes. To assess the influence of DJ-1 on innate immunity signaling in vivo, we have generated djr-1 knockout Caenorhabditis elegans. When grown on pathogenic gram-negative bacteria, djr-1 (-/-) worms showed stronger phosphorylation of p38 mitogen-activated protein kinase (PMK-1) and hyper-induction of PMK-1 target genes. Thus, PD-associated DJ-1 contributes to regulation of innate immunity.
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Leucine-rich repeat kinase 2 induces alpha-synuclein expression via the extracellular signal-regulated kinase pathway.
Cell. Signal.
PUBLISHED: 01-05-2010
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Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most frequent cause of autosomal-dominant Parkinsons disease (PD). The second known autosomal-dominant PD gene (SNCA) encodes alpha-synuclein, which is deposited in Lewy bodies, the neuropathological hallmark of PD. LRRK2 contains a kinase domain with homology to mitogen-activated protein kinase kinase kinases (MAPKKKs) and its activity has been suggested to be a key factor in LRRK2-associated PD. Here we investigated the role of LRRK2 in signal transduction pathways to identify putative PD-relevant downstream targets. Over-expression of wild-type [wt]LRRK2 in human embryonic kidney HEK293 cells selectively activated the extracellular signal-regulated kinase (ERK) module. PD-associated mutants G2019S and R1441C, but not kinase-dead LRRK2, induced ERK phosphorylation to the same extent as [wt]LRRK2, indicating that this effect is kinase-dependent. However, ERK activation by mutant R1441C and G2019S was significantly slower than that for [wt]LRRK2, despite similar levels of expression. Furthermore, induction of the ERK module by LRRK2 was associated to a small but significant induction of SNCA, which was suppressed by treatment with the selective MAPK/ERK kinase inhibitor U0126. This pathway linking the two dominant PD genes LRRK2 and SNCA may offer an interesting target for drug therapy in both familial and sporadic disease.
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Modulation of mitochondrial function and morphology by interaction of Omi/HtrA2 with the mitochondrial fusion factor OPA1.
Exp. Cell Res.
PUBLISHED: 01-04-2010
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Loss of Omi/HtrA2 function leads to nerve cell loss in mouse models and has been linked to neurodegeneration in Parkinsons and Huntingtons disease. Omi/HtrA2 is a serine protease released as a pro-apoptotic factor from the mitochondrial intermembrane space into the cytosol. Under physiological conditions, Omi/HtrA2 is thought to be involved in protection against cellular stress, but the cytological and molecular mechanisms are not clear. Omi/HtrA2 deficiency caused an accumulation of reactive oxygen species and reduced mitochondrial membrane potential. In Omi/HtrA2 knockout mouse embryonic fibroblasts, as well as in Omi/HtrA2 silenced human HeLa cells and Drosophila S2R+ cells, we found elongated mitochondria by live cell imaging. Electron microscopy confirmed the mitochondrial morphology alterations and showed abnormal cristae structure. Examining the levels of proteins involved in mitochondrial fusion, we found a selective up-regulation of more soluble OPA1 protein. Complementation of knockout cells with wild-type Omi/HtrA2 but not with the protease mutant [S306A]Omi/HtrA2 reversed the mitochondrial elongation phenotype and OPA1 alterations. Finally, co-immunoprecipitation showed direct interaction of Omi/HtrA2 with endogenous OPA1. Thus, we show for the first time a direct effect of loss of Omi/HtrA2 on mitochondrial morphology and demonstrate a novel role of this mitochondrial serine protease in the modulation of OPA1. Our results underscore a critical role of impaired mitochondrial dynamics in neurodegenerative disorders.
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Phosphorylation of synucleins by members of the Polo-like kinase family.
J. Biol. Chem.
PUBLISHED: 11-04-2009
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Phosphorylation of alpha-synuclein (alpha-syn) at Ser-129 is a hallmark of Parkinson disease and related synucleinopathies. However, the identity of the natural kinases and phosphatases responsible for regulating alpha-syn phosphorylation remain unknown. Here we demonstrate that three closely related members of the human Polo-like kinase (PLK) family (PLK1, PLK2, and PLK3) phosphorylate alpha-syn and beta-syn specifically at Ser-129 and Ser-118, respectively. Unlike other kinases reported to partially phosphorylate alpha-syn at Ser-129 in vitro, phosphorylation by PLK2 and PLK3 is quantitative (>95% conversion). Only PLK1 and PLK3 phosphorylate beta-syn at Ser-118, whereas no phosphorylation of gamma-syn was detected by any of the four PLKs (PLK1 to -4). PLK-mediated phosphorylation was greatly reduced in an isolated C-terminal fragment (residues 103-140) of alpha-syn, suggesting substrate recognition via the N-terminal repeats and/or the non-amyloid component domain of alpha-syn. PLKs specifically co-localized with phosphorylated Ser-129 (Ser(P)-129) alpha-syn in various subcellular compartments (cytoplasm, nucleus, and membranes) of mammalian cell lines and primary neurons as well as in alpha-syn transgenic mice, especially cortical brain areas involved in synaptic plasticity. Furthermore, we report that the levels of PLK2 are significantly increased in brains of Alzheimer disease and Lewy body disease patients. Taken together, these results provide biochemical and in vivo evidence of alpha-syn and beta-syn phosphorylation by specific PLKs. Our results suggest a need for further studies to elucidate the potential role of PLK-syn interactions in the normal biology of these proteins as well as their involvement in the pathogenesis of Parkinson disease and other synucleinopathies.
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Homo- and heterodimerization of ROCO kinases: LRRK2 kinase inhibition by the LRRK2 ROCO fragment.
J. Neurochem.
PUBLISHED: 08-27-2009
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Mutations in the gene encoding leucine-rich repeat kinase 2 (LRRK2) are the most common cause of autosomal-dominant familial and late-onset sporadic Parkinsons disease (PD). LRRK2 is a large multi-domain protein featuring a GTP-binding C-terminal of Ras of complex proteins (ROC) (ROCO) domain combination unique for the ROCO protein family, directly followed by a kinase domain. Dimerization is a well-established phenomenon among protein kinases. Here, we confirm LRRK2 self-interaction, and provide evidence for general homo- and heterodimerization potential among the ROCO kinase family (LRRK2, LRRK1, and death-associated protein kinase 1). The ROCO domain was critically, though not exclusively involved in dimerization, as a LRRK2 deletion mutant lacking the ROCO domain retained dimeric properties. GTP binding did not appear to influence ROCO(LRRK2) self-interaction. Interestingly, ROCO(LRRK2) fragments exerted an inhibitory effect on both wild-type and the elevated G2019S LRRK2 autophosphorylation activity. Insertion of PD mutations into ROCO(LRRK2) reduced self-interaction and led to a reduction of LRRK2 kinase inhibition. Collectively, these results suggest a functional link between ROCO interactions and kinase activity of wild-type and mutant LRRK2. Importantly, our finding of ROCO(LRRK2) fragment-mediated LRRK2 kinase inhibition offers a novel lead for drug design and thus might have important implications for new therapeutic avenues in PD.
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Knockdown of transactive response DNA-binding protein (TDP-43) downregulates histone deacetylase 6.
EMBO J.
PUBLISHED: 05-28-2009
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TDP-43 is an RNA/DNA-binding protein implicated in transcriptional repression and mRNA processing. Inclusions of TDP-43 are hallmarks of frontotemporal dementia and amyotrophic lateral sclerosis. Besides aggregation of TDP-43, loss of nuclear localization is observed in disease. To identify relevant targets of TDP-43, we performed expression profiling. Thereby, histone deacetylase 6 (HDAC6) downregulation was discovered on TDP-43 silencing and confirmed at the mRNA and protein level in human embryonic kidney HEK293E and neuronal SH-SY5Y cells. This was accompanied by accumulation of the major HDAC6 substrate, acetyl-tubulin. HDAC6 levels were restored by re-expression of TDP-43, dependent on RNA binding and the C-terminal protein interaction domains. Moreover, TDP-43 bound specifically to HDAC6 mRNA arguing for a direct functional interaction. Importantly, in vivo validation in TDP-43 knockout Drosophila melanogaster confirmed the specific downregulation of HDAC6. HDAC6 is necessary for protein aggregate formation and degradation. Indeed, HDAC6-dependent reduction of cellular aggregate formation and increased cytotoxicity of polyQ-expanded ataxin-3 were found in TDP-43 silenced cells. In conclusion, loss of functional TDP-43 causes HDAC6 downregulation and might thereby contribute to pathogenesis.
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Proteasomal inhibition reduces parkin mRNA in PC12 and SH-SY5Y cells.
Parkinsonism Relat. Disord.
PUBLISHED: 04-21-2009
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Mutations in the gene encoding the E3 ubiquitin-protein ligase parkin have been shown to be a common genetic cause of familial early-onset Parkinsons disease (PD). In addition to its function in the ubiquitin-proteasome system (UPS), parkin has been ascribed general neuroprotective properties. Stress and mutation induced decreases in parkin solubility leading to compromised cytoprotection have recently been reported. We systematically investigated whether PD-related stresses including MG132 and epoxomicin (proteasomal impairment), tunicamycin (unfolded protein stress), and rotenone (mitochondrial dysfunction) resulted in expressional changes of parkin and other E3 ubiquitin ligases (dorfin, SIAH-1). Rotenone and tunicamycin did not change parkin mRNA levels, whereas proteasomal inhibition resulted in a reduction of parkin mRNA in PC12 cells as well as in SH-SY5Y cells. Therefore, surprisingly, cells did not react with a compensatory parkin upregulation under proteasomal inhibition, although, in parallel, parkin protein shifted to the insoluble fraction, reducing soluble parkin levels in the cytosol. Since the mRNA of the parkin-coregulated gene PACRG paralleled the parkin mRNA at least partly, we suspect a promoter-driven mechanism. Our study, therefore, shows a link between proteasomal impairment and parkin expression levels in cell culture, which is intriguing in the context of the described and debated proteasomal dysfunction in the substantia nigra of PD patients.
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Parkin deficiency delays motor decline and disease manifestation in a mouse model of synucleinopathy.
PLoS ONE
PUBLISHED: 04-17-2009
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In synucleinopathies, including Parkinsons disease, partially ubiquitylated alpha-synuclein species phosphorylated on serine 129 (P(S129)-alpha-synuclein) accumulate abnormally. Parkin, an ubiquitin-protein ligase that is dysfunctional in autosomal recessive parkinsonism, protects against alpha-synuclein-mediated toxicity in various models.We analyzed the effects of Parkin deficiency in a mouse model of synucleinopathy to explore the possibility that Parkin and alpha-synuclein act in the same biochemical pathway. Whether or not Parkin was present, these mice developed an age-dependent neurodegenerative disorder preceded by a progressive decline in performance in tasks predictive of sensorimotor dysfunction. The symptoms were accompanied by the deposition of P(S129)-alpha-synuclein but not P(S87)-alpha-synuclein in neuronal cell bodies and neuritic processes throughout the brainstem and the spinal cord; activation of caspase 9 was observed in 5% of the P(S129)-alpha-synuclein-positive neurons. As in Lewy bodies, ubiquitin-immunoreactivity, albeit less abundant, was invariably co-localized with P(S129)-alpha-synuclein. During late disease stages, the disease-specific neuropathological features revealed by ubiquitin- and P(S129)-alpha-synuclein-specific antibodies were similar in mice with or without Parkin. However, the proportion of P(S129)-alpha-synuclein-immunoreactive neuronal cell bodies and neurites co-stained for ubiquitin was lower in the absence than in the presence of Parkin, suggesting less advanced synucleinopathy. Moreover, sensorimotor impairment and manifestation of the neurodegenerative phenotype due to overproduction of human alpha-synuclein were significantly delayed in Parkin-deficient mice.These findings raise the possibility that effective compensatory mechanisms modulate the phenotypic expression of disease in parkin-related parkinsonism.
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DJ-1 and prevention of oxidative stress in Parkinsons disease and other age-related disorders.
Free Radic. Biol. Med.
PUBLISHED: 03-20-2009
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Mutations in the PARK7/DJ-1 gene are rare causes of autosomal-recessive hereditary Parkinsons disease. Loss-of-function mutations lead to the characteristic selective neurodegeneration of nigrostriatal dopaminergic neurons, which accounts for parkinsonian symptoms. Originally identified as an oncogene, DJ-1 is a ubiquitous redox-responsive cytoprotective protein with diverse functions. In addition to cell-autonomous neuroprotective roles, DJ-1 may act in a transcellular manner, being up-regulated in reactive astrocytes in chronic neurodegenerative diseases as well as in stroke. Thus, DJ-1, particularly in its oxidized form, has been recognized as a biomarker for cancer and neurodegenerative diseases. The crystal structure of DJ-1 has been solved, allowing detailed investigations of the redox-reactive center of DJ-1. Structure-function studies revealed that DJ-1 may become activated in the presence of reactive oxygen species, under conditions of oxidative stress, but also as part of physiological receptor-mediated signal transduction. DJ-1 regulates redox signaling kinase pathways and acts as a transcriptional regulator of antioxidative gene batteries. Therefore, DJ-1 is an important redox-reactive signaling intermediate controlling oxidative stress after ischemia, upon neuroinflammation, and during age-related neurodegenerative processes. Augmenting DJ-1 activity might provide novel approaches to treating chronic neurodegenerative illnesses such as Parkinsons disease and acute damage such as stroke.
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Oxidizable residues mediating protein stability and cytoprotective interaction of DJ-1 with apoptosis signal-regulating kinase 1.
J. Biol. Chem.
PUBLISHED: 03-16-2009
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Parkinson disease (PD)-associated genomic deletions and the destabilizing L166P point mutation lead to loss of the cytoprotective DJ-1 protein. The effects of other PD-associated point mutations are less clear. Here we demonstrate that the M26I mutation reduces DJ-1 expression, particularly in a null background (knockout mouse embryonic fibroblasts). Thus, homozygous M26I mutation causes loss of DJ-1 protein. To determine the cellular consequences, we measured suppression of apoptosis signal-regulating kinase 1 (ASK1) and cytotoxicity for [M26I]DJ-1, and systematically all other DJ-1 methionine and cysteine mutants. C106A mutation of the central redox site specifically abolished binding to ASK1 and the cytoprotective activity of DJ-1. DJ-1 was apparently recruited into the ASK1 signalosome via Cys-106-linked mixed disulfides. The designed higher order oxidation mimicking [C106DD]DJ-1 non-covalently bound to ASK1 even in the absence of hydrogen peroxide and conferred partial cytoprotection. Interestingly, mutations of peripheral redox sites (C46A and C53A) and M26I also led to constitutive ASK1 binding. Cytoprotective [wt]DJ-1 bound to the ASK1 N terminus (which is known to bind another negative regulator, thioredoxin 1), whereas [M26I]DJ-1 bound to aberrant C-terminal site(s). Consequently, the peripheral cysteine mutants retained cytoprotective activity, whereas the PD-associated mutant [M26I]DJ-1 failed to suppress ASK1 activity and nuclear export of the death domain-associated protein Daxx and did not promote cytoprotection. Thus, cytoprotective binding of DJ-1 to ASK1 depends on the central redox-sensitive Cys-106 and may be modulated by peripheral cysteine residues. We suggest that impairments in oxidative conformation changes of DJ-1 might contribute to PD neurodegeneration.
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Regulation of astrocyte inflammatory responses by the Parkinsons disease-associated gene DJ-1.
FASEB J.
PUBLISHED: 03-10-2009
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The Parkinsons disease (PD)-associated gene DJ-1 mediates direct neuroprotection. The up-regulation of DJ-1 in reactive astrocytes also suggests a role in glia. Here we show that DJ-1 regulates proinflammatory responses in mouse astrocyte-rich primary cultures. When treated with a Toll-like receptor 4 agonist, the bacterial endotoxin lipopolysaccharide (LPS), Dj-1-knockout astrocytes generated >10 times more nitric oxide (NO) than littermate controls. Lentiviral reintroduction of DJ-1 restored the NO response to LPS. The enhanced NO production in Dj-1(-/-) astrocytes was mediated by a signaling pathway involving reactive oxygen species leading to specific hyperinduction of type II NO synthase [inducible NO synthase (iNOS)]. These effects coincided with significantly increased phosphorylation of p38 mitogen-activated protein kinase (MAPK), and p38(MAPK) inhibition suppressed NO production and iNOS mRNA and protein induction. Dj-1(-/-) astrocytes also induced the proinflammatory mediators cyclooxygenase-2 and interleukin-6 significantly more strongly, but not nerve growth factor. Finally, primary neuron cultures grown on Dj-1(-/-) astrocytes became apoptotic in response to LPS in an iNOS-dependent manner, directly demonstrating the neurotoxic potential of astrocytic DJ-1 deficiency. These findings identify DJ-1 as a regulator of proinflammatory responses and suggest that loss of DJ-1 contributes to PD pathogenesis by deregulation of astrocytic neuroinflammatory damage.
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Loss of DJ-1 protein stability and cytoprotective function by Parkinsons disease-associated proline-158 deletion.
J. Neurochem.
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DJ-1 is a ubiquitous protein regulating cellular viability. Recessive mutations in the PARK7/DJ-1 gene are linked to Parkinsons disease (PD). Although the most dramatic L166P point mutation practically eliminates DJ-1 protein and function, the effects of other PD-linked mutations are subtler. Here, we investigated two recently described PD-associated DJ-1 point mutations, the A179T substitution and the P158? in-frame deletion. [A179T]DJ-1 protein was as stable as wild-type [wt]DJ-1, but the P158? mutant protein was less stable. In accord with the notion that dimer formation is essential for DJ-1 protein stability, [P158?]DJ-1 was impaired in dimer formation. Similar to our previous findings for [M26I]DJ-1, [P158?]DJ-1 bound aberrantly to apoptosis signal-regulating kinase 1. Thus, the PD-associated P158? mutation destabilizes DJ-1 protein and function. As there is also evidence for an involvement of DJ-1 in multiple system atrophy, a PD-related ?-synucleinopathy characterized by oligodendroglial cytoplasmic inclusions, we studied an oligodendroglial cell line stably expressing ?-synuclein. ?-Synuclein aggregate dependent microtubule retraction upon co-transfection with tubulin polymerization-promoting protein p25? was ameliorated by [wt]DJ-1. In contrast, DJ-1 mutants including P158? failed to protect in this system, where we found evidence of apoptosis signal-regulating kinase 1 (ASK1) involvement. In conclusion, the P158? point mutation may contribute to neurodegeneration by protein destabilization and hence loss of DJ-1 function.
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Impaired c-Fos and polo-like kinase 2 induction in the limbic system of fear-conditioned ?-synuclein transgenic mice.
PLoS ONE
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?-Synuclein (?SYN) is genetically and neuropathologically linked to a spectrum of neurodegenerative diseases including Parkinsons disease, dementia with Lewy bodies, and related disorders. Cognitive impairment is recapitulated in several ?SYN transgenic mouse lines. However, the mechanisms of dysfunction in affected neurons are largely unknown. Here we measured neuronal activity induced gene products in the limbic system of ?SYN transgenic mice upon fear conditioning (FC). Induction of the synaptic plasticity marker c-Fos was significantly reduced in the amygdala and hippocampus of (Thy1)-h[A30P]?SYN transgenic mice in an age-dependent manner. Similarly, the neuronal activity inducible polo-like kinase 2 (Plk2) that can phosphorylate ?SYN at the pathological site serine-129 was up-regulated in both brain regions upon FC. Plk2 inductions were also significantly impaired in aged (Thy1)-h[A30P]?SYN transgenic mice, both in the amygdala and hippocampus. Plk2 inductions in the amygdala after FC were paralleled by a small but significant increase in the number of neuronal cell bodies immunopositive for serine-129 phosphorylated ?SYN in young but not aged (Thy1)-h[A30P]?SYN transgenic mice. In addition, we observed in the aged hippocampus a distinct type of apparently unmodified transgenic ?SYN profiles resembling synaptic accumulations of ?SYN. Thus, the cognitive decline observed in aged ?SYN transgenic mice might be due to impairment of neurotransmission and synaptic plasticity in the limbic system by distinct ?SYN species.
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Toll-like receptors 2 and 4 impair insulin-mediated brain activity by interleukin-6 and osteopontin and alter sleep architecture.
FASEB J.
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Impaired insulin action in the brain represents an early step in the progression toward type 2 diabetes, and elevated levels of saturated free fatty acids are known to impair insulin action in prediabetic subjects. One potential mediator that links fatty acids to inflammation and insulin resistance is the Toll-like receptor (TLR) family. Therefore, C3H/HeJ/TLR2-KO (TLR2/4-deficient) mice were fed a high-fat diet (HFD), and insulin action in the brain as well as cortical and locomotor activity was analyzed by using telemetric implants. TLR2/4-deficient mice were protected from HFD-induced glucose intolerance and insulin resistance in the brain and displayed an improvement in cortical and locomotor activity that was not observed in C3H/HeJ mice. Sleep recordings revealed a 42% increase in rapid eye movement sleep in the deficient mice during daytime, and these mice spent 41% more time awake during the night period. Treatment of control mice with a neutralizing IL-6 antibody improved insulin action in the brain as well as cortical activity and diminished osteopontin protein to levels of the TLR2/4-deficient mice. Together, our data suggest that the lack of functional TLR2/4 protects mice from a fat-mediated impairment in insulin action, brain activity, locomotion, and sleep architecture by an IL-6/osteopontin-dependent mechanism.
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