Specific up-regulation of GADD153/CHOP in 1-methyl-4-phenyl-pyridinium-treated SH-SY5Y cells

Echinacoside Protects Against MPP(+)-Induced Neuronal Apoptosis via ROS/ATF3/CHOP Pathway Regulation

Echinacoside (ECH) is protective in a mouse model of Parkinson's disease (PD) induced by 1-methyl-4-phenylpyridinium ion (MPP(+)). To investigate the mechanisms involved, SH-SY5Y neuroblastoma cells were treated with MPP(+) or a combination of MPP(+) and ECH, and the expression of ATF3 (activating transcription factor 3), CHOP (C/EBP-homologous protein), SCNA (synuclein alpha), and GDNF (glial cell line-derived neurotrophic factor) was assessed. The results showed that ECH significantly improved cell survival by inhibiting the generation of MPP(+)-induced reactive oxygen species (ROS). In addition, ECH suppressed the ROS and MPP(+)-induced expression of apoptotic genes (ATF3, CHOP, and SCNA). ECH markedly decreased the MPP(+)-induced caspase-3 activity in a dose-dependent manner. ATF3-knockdown also decreased the CHOP and cleaved caspase-3 levels and inhibited the apoptosis induced by MPP(+). Interestingly, ECH partially restored the GDNF expression that was down-regulated by MPP(+). ECH also improved dopaminergic neuron survival during MPP(+) treatment and protected these neurons against the apoptosis induced by MPTP. Taken together, these data suggest that the ROS/ATF3/CHOP pathway plays a critical role in mechanisms by which ECH protects against MPP(+)-induced apoptosis in PD.

Neurotoxin-induced pathway perturbation in human neuroblastoma SH-EP cells

The exact causes of cell death in Parkinson's disease (PD) remain unknown despite extensive studies on PD.The identification of signaling and metabolic pathways involved in PD might provide insight into the molecular mechanisms underlying PD. The neurotoxin 1-methyl-4-phenylpyridinium (MPP(+)) induces cellular changes characteristic of PD, and MPP(+)-based models have been extensively used for PD studies. In this study, pathways that were significantly perturbed in MPP(+)-treated human neuroblastoma SH-EP cells were identified from genome-wide gene expression data for five time points (1.5, 3, 9, 12, and 24 h) after treatment. The mitogen-activated protein kinase (MAPK) signaling pathway and endoplasmic reticulum (ER) protein processing pathway showed significant perturbation at all time points. Perturbation of each of these pathways resulted in the common outcome of upregulation of DNA-damage-inducible transcript 3 (DDIT3). Genes involved in ER protein processing pathway included ubiquitin ligase complex genes and ER-associated degradation (ERAD)-related genes. Additionally, overexpression of DDIT3 might induce oxidative stress via glutathione depletion as a result of overexpression of CHAC1. This study suggests that upregulation of DDIT3 caused by perturbation of the MAPK signaling pathway and ER protein processing pathway might play a key role in MPP(+)-induced neuronal cell death. Moreover, the toxicity signal of MPP(+) resulting from mitochondrial dysfunction through inhibition of complex I of the electron transport chain might feed back to the mitochondria via ER stress. This positive feedback could contribute to amplification of the death signal induced by MPP(+).

Increase in endoplasmic reticulum-associated tissue transglutaminase and enzymatic activation in a cellular model of Parkinson's disease

Parkinson's disease (PD) is characterized by accumulation of α-synuclein aggregates and degeneration of melanized, catecholaminergic neurons. The tissue transglutaminase (tTG) enzyme catalyzes molecular protein cross-linking. In PD, tTG levels are increased and cross-linking has been identified as an important factor in α-synuclein aggregation. In our quest to link tTGs distribution in the human brain to the hallmarks of PD pathology, we recently reported that catecholaminergic neurons in PD disease-affected brain areas display typical endoplasmic reticulum (ER) granules showing tTG immunoreactivity. In the present study, we set out to elucidate the nature of the interaction between tTG and the ER in PD pathogenesis, using retinoic-acid differentiated SH-SY5Y cells exposed to the PD-mimetic 1-methyl-4-phenylpyridinium (MPP(+)). Alike our observations in PD brain, MPP(+)-treated cells displayed typical TG-positive granules, that were also induced by other PD mimetics and by ER-stress inducing toxins. Additional immunocytochemical and biochemical investigation revealed that tTG is indeed associated to the ER, in particular at the cytoplasmic face of the ER. Upon MPP(+) exposure, additional recruitment of tTG toward the ER was found. In addition, we observed that MPP(+)-induced tTG activity results in transamidation of ER membrane proteins, like calnexin. Our data provide strong evidence for a, so far unrecognized, localization of tTG at the ER, at least in catecholaminergic neurons, and suggests that in PD activation of tTG may have a direct impact on ER function, in particular via post-translational modification of ER membrane proteins.

Upregulation of GADD153 by butyrate: involvement of MAPK

Butyrate inhibits the proliferation of cancer cells, but the early molecular events initiated by butyrate have not been fully identified. Herein, butyrate is shown to affect the growth arrest and DNA damage-inducible gene 153 (GADD153) in HCT-116 human colon adenocarcinoma cells. Despite absence of any detectable cellular DNA damage, the expression of GADD153 was upregulated before several features characteristic of apoptosis appeared. Butyrate-induced upregulation of GADD153 mRNA was attenuated by actinomycin D, but apparently not by cycloheximide. In investigating possible involvement of MAPK in mediating the effect of butyrate on GADD153 mRNA expression, the extracellular regulated kinase (ERK) inhibitor PD98059, but neither the JNK inhibitor SP600125 nor the p38 MAPK inhibitor SB203580, blunted the ability of butyrate to upregulate GADD153 mRNA expression. U0126, a selective inhibitor of upstream MEK, had a similar effect as PD98059 on butyrate-induced GADD153 mRNA upregulation. Collectively, these findings suggest that butyrate caused activation of the GADD153 gene at the level of transcription involving mainly the MEK/ERK branch of the MAPK signal transduction pathway. Moreover, these molecular events were not the result of any DNA damage and occurred before several features characteristic of apoptosis became evident.

Sequential and concerted gene expression changes in a chronic in vitro model of parkinsonism

Many mechanisms of neurodegeneration have been implicated in Parkinson's disease, but which ones are most important and potential interactions among them are unclear. To provide a broader perspective on the parkinsonian neurodegenerative process, we have performed a global analysis of gene expression changes caused by chronic, low-level exposure of neuroblastoma cells to the mitochondrial complex I inhibitor and parkinsonian neurotoxin rotenone. Undifferentiated SK-N-MC human neuroblastoma cells were grown in the presence of rotenone (5 nM), and RNA was extracted at three different time points (baseline, 1 week, and 4 weeks) for labeling and hybridization to Affymetrix Human U133 Plus 2.0 GeneChips. Our results show that rotenone induces concerted alterations in gene expression that change over time. Particularly, alterations in transcripts related to DNA damage, energy metabolism, and protein metabolism are prominent during chronic complex I inhibition. These data suggest that early augmentation of capacity for energy production in response to mitochondrial inhibition might be deleterious to cellular function and survival. These experiments provide the first transcriptional analysis of a rotenone model of Parkinson's disease and insight into which mechanisms of neurodegeneration may be targeted for therapeutic intervention.

Microarray analysis of oxidative stress regulated genes in mesencephalic dopaminergic neuronal cells: relevance to oxidative damage in Parkinson's disease

Oxidative stress and apoptotic cell death have been implicated in the dopaminergic cell loss that characterizes Parkinson's disease. While factors contributing to apoptotic cell death are not well characterized, oxidative stress is known to activate an array of cell signaling molecules that participate in apoptotic cell death mechanisms. We investigated oxidative stress-induced cytotoxicity of hydrogen peroxide (H2O2) in three cell lines, the dopaminergic mesencephalon-derived N27 cell line, the GABAergic striatum-derived M213-20 cell line, and the hippocampal HN2-5 cell line. N27 cells were more sensitive to H2O2-induced cell death than M213-20 and HN2-5 cells. H2O2 induced significantly greater increases in caspase-3 activity in N27 cells than in M213-20 cells. H2O2-induced apoptotic cell death in N27 cells was mediated by caspase-3-dependent proteolytic activation of PKCdelta. Gene expression microarrays were employed to examine the specific transcriptional changes in N27 cells exposed to 100 microM H2O2 for 4 h. Changes in genes encoding pro- or anti-apoptotic proteins included up-regulation of BIK, PAWR, STAT5B, NPAS2, Jun B, MEK4, CCT7, PPP3CC, and PSDM3, while key down-regulated genes included BNIP3, NPTXR, RAGA, STK6, YWHAH, and MAP2K1. Overall, the changes indicate a modulation of transcriptional activity, chaperone activity, kinase activity, and apoptotic activity that appears highly specific, coordinated and relevant to cell survival. Utilizing this in vitro model to identify novel oxidative stress-regulated genes may be useful in unraveling the molecular mechanisms underlying dopaminergic degeneration in Parkinson's disease.

Mitochondrial uncoupling protein-4 regulates calcium homeostasis and sensitivity to store depletion-induced apoptosis in neural cells

An increase in the cytoplasmic-free Ca(2+) concentration mediates cellular responses to environmental signals that influence a range of processes, including gene expression, motility, secretion of hormones and neurotransmitters, changes in energy metabolism, and apoptosis. Mitochondria play important roles in cellular Ca(2+) homeostasis and signaling, but the roles of specific mitochondrial proteins in these processes are unknown. Uncoupling proteins (UCPs) are a family of proteins located in the inner mitochondrial membrane that can dissociate oxidative phosphorylation from respiration, thereby promoting heat production and decreasing oxyradical production. Here we show that UCP4, a neuronal UCP, influences store-operated Ca(2+) entry, a process in which depletion of endoplasmic reticulum Ca(2+) stores triggers Ca(2+) influx through plasma membrane "store-operated" channels. PC12 neural cells expressing human UCP4 exhibit reduced Ca(2+) entry in response to thapsigargin-induced endoplasmic reticulum Ca(2+) store depletion. The elevations of cytoplasmic and intramitochondrial Ca(2+) concentrations and mitochondrial oxidative stress induced by thapsigargin were attenuated in cells expressing UCP4. The stabilization of Ca(2+) homeostasis and preservation of mitochondrial function by UCP4 was correlated with reduced mitochondrial reactive oxygen species generation, oxidative stress, and Gadd153 up-regulation and increased resistance of the cells to death. Reduced Ca(2+)-dependent cytosolic phospholipase A2 activation and oxidative metabolism of arachidonic acid also contributed to the stabilization of mitochondrial function in cells expressing human UCP4. These findings demonstrate that UCP4 can regulate cellular Ca(2+) homeostasis, suggesting that UCPs may play roles in modulating Ca(2+) signaling in physiological and pathological conditions.

Intranigral Dopamine Toxicity and α-Synuclein Response in Rats

There is increasing evidence that, in addition to its function as the main neurotransmitter in the nigrostriatal pathway, dopamine (DA) may be neurotoxic in certain conditions. In this study, the toxicity of DA was assessed by direct injection into the substantia nigra of anaesthetised rats, and its effects were compared with those of 6-hydroxydopamine. Brains were removed 1, 2 and 3 weeks after the lesion for histological or neurochemical analysis. DA caused a significant loss of 35% of tyrosine hydroxylase-positive neurons in the pars compacta of substantia nigra and a 40% reduction of striatal DA content. Cells with signs compatible with both apoptosis and autophagy were observed. GADD153, a parameter of endoplasmic reticulum stress, was strongly induced by 6-hydroxydopamine but not by DA. DA increased the alpha-synuclein content 1 week after the lesion (but not at the later times analyzed) in tyrosine hydroxylase-positive and in non-dopaminergic fibers of pars reticulata. The alpha-synuclein increase may be a physiological temporal response to DA accumulation and/or to cell damage, but the simultaneous presence of alpha-synuclein and DA in the cell cytoplasm at concentration higher than normal is not exempt from risk. In fact, their incubation in a free cell system gives a stable dimerized form of alpha-synuclein that has been described as the critical rate-limiting step for its abnormal fibrillation.

Identification of the protein disulfide isomerase family member PDIp in experimental Parkinson's disease and Lewy body pathology

Parkinson's disease (PD) is a slowly progressing neurodegenerative disorder with no clear etiology. Pathological hallmarks of the disease include the loss of dopaminergic neurons from the substantia nigra (SN) and the presence of Lewy bodies (LBs) (alpha-synuclein and ubiquitin-positive, eosinophilic, cytoplasmic inclusions) in many of the surviving neurons. Experimental modeling of PD neurodegeneration using the neurotoxins 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and 1-methyl-4-phenyl-pyridinium (MPP(+)) has identified changes in gene expression of different endoplasmic reticulum (ER) stress proteins associated with MPTP- and PD-related neurodegeneration. We show that the protein disulfide isomerase (PDI) family member pancreatic protein disulfide isomerase (PDIp), previously considered exclusively expressed in pancreatic tissue, is uniquely upregulated among PDI family members within 24 h following exposure of retinoic acid (RA)-differentiated SH-SY5Y human neuroblastoma cells to either 1 mM MPP(+) or 10 microM of the highly specific proteasome inhibitor lactacystin. RT-PCR confirms PDIp expression in brain of post-mortem human PD subjects and immunohistochemical studies demonstrate PDIp immunoreactivity in LBs. Collectively, these findings suggest that increased PDIp expression in dopaminergic (DA) neurons might contribute to LB formation and neurodegeneration, and that this increased PDIp expression may be the result of proteasome impairment.

The C/EBP homologous protein CHOP (GADD153) is an inhibitor of Wnt/TCF signals

CHOP (GADD153) is a protein of the C/EBP family of transcriptional regulators, which dimerizes with other C/EBP members and changes their DNA-binding and transactivation properties. It induces growth arrest and apoptosis after endoplasmatic reticulum stress or DNA damage. CHOP is also expressed during early embryogenesis and upregulated in tumour tissues with defective Wnt signals. We report here that CHOP functions as a specific inhibitor of Wnt/T-cell factor (TCF) signalling. CHOP inhibits TCF-dependent transcription in human embryonic and colon cancer cell lines. Injection of CHOP mRNA into early Xenopus laevis embryos suppresses dorsal organizer formation and inhibits secondary axis formation and TCF-dependent transcription in response to Wnt-8, Dishevelled, beta-Catenin and TCF-VP16. In embryos and human cells, this inhibition depends on the N-terminal transactivation domain of CHOP, whereas the C-terminal dimerization domain is dispensable. CHOP binds to TCF factors, thereby preventing the binding of TCF to its DNA recognition site. Our findings demonstrate a novel function of CHOP as a Wnt repressor.

Induction of C/EBP beta and GADD153 expression by dopamine in human neuroblastoma cells. Relationship with alpha-synuclein increase and cell damage

Expression of CCAAT/enhancer-binding protein beta (C/EBP beta) and growth-arrest DNA damage-inducible 153/C/EBP beta homology protein (GADD153/CHOP) increased after incubation of human neuroblastoma SH-SY5Y cells with a range of dopamine concentrations. Dopamine (100 microM) caused an increase in C/EBP beta expression between 2 and 12 h of treatment, with no evident intracellular morphological changes. Dopamine (500 microM) led to the appearance of autophagic-like vacuoles and a marked increase in GADD153/CHOP between 6 and 24 h of treatment. The expression of alpha-synuclein, the main protein of Lewy bodies in Parkinson's disease and other neurological disorders, increased with a profile similar to C/EBP beta. In addition, overexpression of C/EBP beta caused a concomitant increase in the expression of alpha-synuclein but not of GADD153. In contrast, the overexpression of GADD153 did not alter the expression of alpha-synuclein. Inhibition of JNK by SP600125 reduced increases in C/EBP beta and alpha-synuclein expression, whereas inhibition of both JNK and p38MAPK (with SB203580) blocked the increase in GADD153 expression. We conclude that dopamine, through a mechanism driven by stress-activated MAPKs, triggers C/EBP beta and GADD153 expression in a dose-dependent way. Given that the promoter region of the alpha-synuclein gene contains distinct zones that are susceptible to regulation by C/EBP beta, this factor could be involved in the increased expression of alpha-synuclein after dopamine-induced cell stress. GADD153 increase seems to be related with the endoplasmic reticulum stress, autophagy and cell death observed at high dopamine concentrations.

Increased GADD gene expression in human colon epithelial cells exposed to deoxycholate

The colonic epithelium is often exposed to high concentrations of secondary bile acids, which stresses the epithelial cells, leading potentially to activation of stress-response genes. To examine this possibility in vitro, the purpose of this study was to determine if expression of certain growth arrest and DNA damage-inducible genes (GADD) is upregulated in human colonic epithelial cells exposed to deoxycholate (DOC). DNA macroarray screening of a small cluster of stress/apoptosis-related genes in DOC-treated HCT-116 colonocytes revealed clearly higher expression of only GADD45, which was confirmed by gene-specific relative RT-PCR analysis. Subsequently, it was found that DOC also increased GADD34 mRNA expression. However, mRNA expression of GADD153 was increased most markedly in DOC-treated HCT-116 colonocytes, which express wild-type p53. However, the upregulation of GADD34, GADD45, and GADD153 mRNA expression apparently did not require p53, based on the finding that DOC increased expression of all three GADD genes in HCT-15 colonocytes, which express mutant p53. In further studying GADD153 in particular, the effect of DOC on GADD153 mRNA was prevented by actinomycin-D (Act-D), but not by antioxidants or MAPK inhibitors. DOC also caused GADD153 protein to be expressed in close parallel with increased GADD153 mRNA expression. Induction of GADD153 protein by DOC was prevented by either anisomycin or cycloheximide. These findings suggest that DOC-induced upregulation of GADD153 mRNA expression occurred at the level of transcription without involving reactive oxygen species and MAPK signaling, and that the expression of GADD153 protein was due also to translation of pre-existing, and not just newly synthesized, mRNA.

Upregulation of clusterin/apolipoprotein J in lactacystin-treated SH-SY5Y cells

Clusterin (apolipoprotein J) is a highly conserved, multifunctional, vertebrate glycoprotein. Several isoforms of clusterin have been described including the predominant secreted isoform (sCLU) and several nuclear isoforms (nCLU) associated with cell death. sCLU has been shown to bind a variety of partly unfolded, stressed proteins including those associated with Lewy bodies (LBs) in patients with Parkinson's disease (PD). The development of familial and sporadic PD has been associated with the ubiquitin-proteasome system (UPS) dysfunction and aberrant protein degradation. This suggests that failure of the UPS to degrade abnormal proteins may underlie nigral degeneration and LB formation in PD. The effects of toxin-mediated proteasomal impairment on changes in gene expression and cell viability were studied in differentiated SH-SY5Y cells. Clusterin expression was increased in cells exposed for 24 hr to the proteasomal inhibitor lactacystin (10 microM) as determined by gene microarray analysis. RT-PCR showed that sCLU, not nCLU, was the major clusterin isoform expressed in both control and lactacystin-treated cells. Western blot analysis identified statistically significant increases in sCLU in total cell lysates after 24 hr of lactacystin exposure and showed that sCLU fractionates with the endoplasmic reticulum. Time-course studies demonstrated that maximal decreases in proteasome activity (4 hr) preceded maximal increases in clusterin expression (24 hr). Together these data suggest that proteasome impairment results in the upregulation of sCLU in SH-SY5Y cells, supporting the hypothesis that the association of clusterin with LBs in PD may be related to UPS failure.

Insulin degrading enzyme is expressed in the human cerebrovascular endothelium and in cultured human cerebrovascular endothelial cells

Insulin degrading enzyme (IDE) is found in the cytosol, peroxisomes and plasma membrane of many cells. Although it preferentially cleaves insulin it can also cleave many other small proteins with diverse sequences including the monomeric form of the amyloid beta peptide (A beta). In the brain, IDE has been reported to be expressed predominantly in neurons. In this study, IDE expression was detected in cultured human cerebrovascular endothelial cells. Using laser capture microdissection followed by PCR analysis, it was found that IDE mRNA is expressed in human brain blood vessels. Using immunofluorescence and multiphoton microscopy IDE was localized to the endothelium of the cerebrovascular blood vessels in human.

Increased GADD153 gene expression during iron chelation-induced apoptosis in Jurkat T-lymphocytes

Depriving cells of iron likely stresses them and can result in cell death. To examine the potential relationship between this form of stress and cell death, Jurkat T-lymphocytes were made iron-deficient by exposing them to the iron chelator, deferoxamine (DFO). Such treatment produced evidence of apoptosis, including cell shrinkage, membrane blebbing, chromatin condensation and fragmentation, and also formation of apoptotic bodies. Additionally, proteolytic cleavage of poly(ADP-ribose)polymerase was detected, suggesting involvement of caspases in initiating apoptosis. Indeed, a selective caspase-3 inhibitor prevented the effects of DFO. During the early induction period of apoptosis, GRP78 and HSP70 mRNA expression was not affected. In contrast, there was mainly increased mRNA expression of Growth Arrest and DNA Damage-inducible gene 153 (GADD153), which seemed to be at the level of transcription rather than mRNA stability. Furthermore, fortifying cells with antioxidants did not prevent the increased GADD153 mRNA expression, and no evidence of single-strand breaks in DNA was found, suggesting that neither reactive oxygen species nor DNA damage was involved in triggering GADD153 gene activation. DFO also caused GADD153 protein to be expressed. Because GADD153 is recognized as a pro-apoptotic gene, these findings generate the notion that GADD153 might help mediate apoptosis in iron-deficient cells.

cDNA microarray analysis of changes in gene expression associated with MPP+ toxicity in SH-SY5Y cells

cDNA microarray analysis of 1-methyl-4-phenyl-pyridinium (MPP+) toxicity (1 mM, 72 h) in undifferentiated SH-SY5Y cells identified 48 genes that displayed a signal intensity greater than the mean of all differentially expressed genes and a two-fold or greater difference in normalized expression. RT-PCR analysis of a subset of genes showed that c-Myc and RNA-binding protein 3 (RMB3) expression decreased by approximately 50% after 72 h of exposure to MPP+ (1 mM) but did not change after 72 h of exposure to 6-hydroxydopamine (25 microM), rotenone (50 nM), and hydrogen peroxide (600 microM). Exposure of retinoic acid (RA)-differentiated SH-SY5Y cells to MPP+ (1 mM, 72 h) also resulted in a decrease in RMB3 expression and an increase in GADD153 expression. In contrast, c-Myc expression was slightly increased in RA-differentiated cells. Collectively, these data provide new insights into the molecular mechanisms of MPP+ toxicity and show that MPP+ can elicit distinct patterns of gene expression in undifferentiated and RA-differentiated SH-SY5Y cells.

Induction of GADD gene expression by phenethylisothiocyanate in human colon adenocarcinoma cells

Phenethylisothiocyanate (PEITC), a potential cancer chemopreventive agent, induces colon cancer cell death, but the mechanism is not entirely clear. Therefore, the aim of this study was to further clarify the molecular effects of PEITC in causing death of human colon adenocarcinoma cells. When incubated with PEITC, HCT-116 colonocytes showed morphological features characteristic of apoptosis, such as irregular cell shape, translocation of plasma membrane phosphatidylserine, and also chromatin condensation and fragmentation. These changes occurred after single-strand breaks in DNA were detected, suggesting that PEITC induced irreparable DNA damage, which in turn triggered the process of apoptosis. DNA macroarray analysis of a selected small cluster of apoptosis-related genes revealed noticeably higher expression of only GADD45, which was confirmed by gene-specific relative RT-PCR analysis. This led to investigation of other GADD gene members possibly affected by PEITC. Whereas GADD34 mRNA expression increased just slightly, there was an appreciable elevation of the mRNA for GADD153, which is recognized as a pro-apoptotic gene. The effect of PEITC on GADD153 was attenuated by either actinomycin D or N-acetylcysteine, suggesting that PEITC-induced upregulation of GADD153 mRNA expression was partly at the level of transcriptional activation involving reactive oxygen species. Additionally, PEITC-induced upregulation of GADD153 mRNA expression did not appear to require p53, based on the observation that PEITC also increased GADD153 mRNA expression in HCT-15 colonocytes, which are known to express mutant p53. These findings suggest that PEITC creates an oxidative cellular environment that induces DNA damage and GADD153 gene activation, which in turn helps trigger apoptosis.

MPP+Induces the Endoplasmic Reticulum Stress Response in Rabbit Brain Involving Activation of the ATF-6 and NF-κB Signaling Pathways

Inhibition of mitochondrial function and the subsequent generation of oxidative stress are strongly suggested to underlie MPTP/MPP+-induced neurotoxicity, which has been used extensively as a model for Parkinson disease. In the present study we have examined the hypothesis that MPP+ targets the endoplasmic reticulum. Because rabbits possess more genetic similarities to primates than to rodents we have selected this animal model system for our MPP+ neurotoxicity studies. MPP+ was administered directly into the brain of New Zealand white rabbits via the intracisternal route, and the effects on tissue from the substantia nigra were examined. Here we demonstrate that MPP+ in a dose-dependent manner induces the loss of tyrosine hydroxylase activity, oxidative DNA damage, and activation of the endoplasmic reticulum stress response. The endoplasmic reticulum response, mediated by activation of ATF-6 and NF-kappaB, leads to activation of gadd 153. These effects correlate with the activation of caspase-3 and of c-Jun N-terminal kinase (JNK) kinase. We propose that pharmacological agents that inhibit the perturbation of endoplasmic reticulum function or the activation of JNK may represent a potential therapeutic approach for the prevention of neurotoxin-induced Parkinson disease.

Functional genomics and proteomics in control of breathing

New genomic and proteomic techniques offer remarkable promise as tools to address longstanding questions regarding molecular mechanisms involved in the control of breathing. Here, these techniques are described. Additionally, recent examples of the application of these and related molecular techniques are provided-particularly including observations regarding the role of S-nitrosylation signaling reactions in regulating ventilatory responses.

Parkinsonian mimetics induce aspects of unfolded protein response in death of dopaminergic neurons

Genes associated with Parkinson's disease (PD) have suggested a role for ubiquitin-proteasome dysfunction and aberrant protein degradation in this disorder. Inasmuch as oxidative stress has also been implicated in PD, the present study examined transcriptional changes mediated by the Parkinsonism-inducing neurotoxins 6-hydroxydopamine (6-OHDA) and 1-methyl-4-phenylpyridinium (MPP+) in a dopaminergic cell line. Microarray analysis of RNA isolated from toxin treated samples revealed that the stress-induced transcription factor CHOP/Gadd153 was dramatically up-regulated by both 6-OHDA and MPP+. Treatment with 6-OHDA also induced a large number of genes involved in endoplasmic reticulum stress and unfolded protein response (UPR) such as ER chaperones and elements of the ubiquitin-proteasome system. Reverse transcription-PCR, Western blotting, and immunocytochemical approaches were used to quantify and temporally order the UPR pathways involved in neurotoxin-induced cell death. 6-OHDA, but not MPP+, significantly increased hallmarks of UPR such as BiP, c-Jun, and processed Xbp1 mRNA. Both toxins increased the phosphorylation of UPR proteins, PERK and eIF2 alpha, but only 6-OHDA increased phosphorylation of c-Jun. Thus, 6-OHDA is capable of triggering multiple pathways associated with UPR, whereas MPP+ exhibits a more restricted response. The involvement of UPR in these widely used neurotoxin models supports the role of ubiquitin-proteasome pathway dysfunction in PD.

Dependence on electron transport chain function and intracellular signaling of genomic responses in SH-SY5Y cells to the mitochondrial neurotoxin MPP(+)

SH-SY5Y neuroblastoma cells exposed to the complex I inhibitor/parkinsonian neurotoxin methylpyridinium ion (MPP(+)) activate both survival and death-promoting signaling pathways and undergo MEK/ERK-dependent, phosphatidylinositol-3 kinase-dependent, and c-Jun kinase-dependent cell death. Because genomic responses to MPP(+) are not extensively characterized, we used nylon cDNA arrays to measure gene expression following exposure to an apoptosis-producing [MPP(+)]. Many changes occurred within 5 min, and all gene expression changes appeared before biochemical and morphological markers of apoptosis. The majority of gene expression changes in SY5Y were not found in rho(0) cells, indicating dependence of these changes on intact electron transport activity. rho(0) cells exposed to MPP(+) produced different expression profiles, indicating the potential for responses independent of complex I inhibition. MPP(+)-induced gene expression patterns in normal SY5Y cells were sensitive to inhibitors of MEK/ERK (UO 126) or phosphatidylinositol-3 kinase (LY 294002), demonstrating regulation of gene expression by these survival-promoting signaling pathways. The primary signaling molecules mediating these MPP(+)-induced gene expression changes are unknown but ultimately utilize MEK/ERK and phosphatidylinositol-3 kinase signaling. Genes suppressed by UO 126 or LY 294002 during MPP(+) exposure may mediate cell survival; those expressed in the presence of UO 126 or LY 294002 may mediate cell death in this in vitro model of Parkinson's disease.