Microarray expression profiling identifies early signaling transcripts associated with 6-OHDA-induced dopaminergic cell death

Physiological/pathological ramifications of transcription factors in the unfolded protein response

Numerous environmental, physiological, and pathological insults disrupt protein-folding homeostasis in the endoplasmic reticulum (ER), referred to as ER stress. Eukaryotic cells evolved a set of intracellular signaling pathways, collectively termed the unfolded protein response (UPR), to maintain a productive ER protein-folding environment through reprogramming gene transcription and mRNA translation. The UPR is largely dependent on transcription factors (TFs) that modulate expression of genes involved in many physiological and pathological conditions, including development, metabolism, inflammation, neurodegenerative diseases, and cancer. Here we summarize the current knowledge about these mechanisms, their impact on physiological/pathological processes, and potential therapeutic applications.

Effects of Simazine Exposure on Neuronal Development-Related Factors in MN9D Cells

Background

Simazine is a triazine herbicide used worldwide in both agricultural and non-agricultural fields that is frequently detected in surface water and groundwater. Due to its widespread use, an increasing amount of research has focused on the potentially serious environmental and health risks.

Material/Methods

We used Western blotting and real-time quantitative PCR to analyze the effects of simazine on dopamine neuronal development-related factors in MN9D dopaminergic cells.

Results

The expression of tyrosine hydroxylase (TH) mRNA was significantly increased after treatment with 300 and 600 μmol L⁻¹ simazine after 24 and 48 h. Levels of nuclear-related receptor 1 (Nurr1) mRNA after 24- and 48-h exposure were decreased with 50 μmol L⁻¹ simazine, but increased with 600 μmol L⁻¹ simazine. Significant increases in TH and Nurr1 protein were observed in all simazine-treated groups at 24 and 48 h. The expression of neurogenin 2 and LIM homeobox transcription factor 1 beta (Lmx1b) mRNA were significantly increased after exposure to 600 μmol L⁻¹ simazine for 48 h, while the expression of wingless-type MMTV integration site family member 1 (Wnt1) mRNA was increased by all doses of simazine.

Conclusions

Simazine may have an impact on TH in MN9D cells through 2 mechanisms; one mechanism is through the Lmx1a/Ngn2 pathway, and the other mechanism is through the Lmx1b-pitx3/Wnt1-Nurr1 pathway. These 2 pathways likely do not operate in isolation, but rather together, during the cellular response to simazine exposure.

Analysis of hippocampal gene expression profile of Alzheimer's disease model rats using genome chip bioinformatics

In this study, an Alzheimer's disease model was established in rats through stereotactic injection of condensed amyloid beta 1–40 into the bilateral hippocampus, and the changes of gene expression profile in the hippocampus of rat models and sham-operated rats were compared by genome expression profiling analysis. Results showed that the expression of 50 genes was significantly up-regulated (fold change ≥ 2), while 21 genes were significantly down-regulated in the hippocampus of Alzheimer's disease model rats (fold change ≤ 0.5) compared with the sham-operation group. The differentially expressed genes are involved in many functions, such as brain nerve system development, neuronal differentiation and functional regulation, cellular growth, differentiation and apoptosis, synaptogenesis and plasticity, inflammatory and immune responses, ion channels/transporters, signal transduction, cell material/energy metabolism. Our findings indicate that several genes were abnormally expressed in the metabolic and signal transduction pathways in the hippocampus of amyloid beta 1–40-induced rat model of Alzheimer's disease, thereby affecting the hippocampal and brain functions.

Effect of Tiantai No.1 on gene expression profiles in hippocampus of Alzheimer's disease rats by bioinformatic analysis

OBJECTIVE

To study the effect of Tiantai No. 1 [symbol in text] on gene expression profile in hippocampus of Alzheimer's disease (AD) rat, molecular genetic target points of the effect of this drug were defined, its molecular genetic pharmacodynamic mechanism of anti-AD was further explored at molecular gene level, and a scientific basis was provided for its clinical availability and promotion.

METHODS

Thirty male Sprague-Dawley rats were divided into three groups with 10 rats per group: sham-operation group, model group and Tiantai No. 1 group. Sterile surgical procedure was applied, the model group with bilateral hippocampal injection of Aβ1-40 was established, and normal saline was used instead of Aβ1-40 in the sham-operation group. One week after the models was made, rats were administered by gastric lavage once every day for three consecutive weeks. The rats of the sham-operation group and the model group were daily fed with purified water by lavage; the rats of the Tiantai No.1 group treated group were administered with Tiantai No.1 by lavage. Total RNAs of hippocampus tissues were extracted with Trizol, the changes of hippocampus gene expression profiles in the above three groups were analyzed by using Affymetrix rat whole genome expression profile microarray.

RESULTS

Microarray analysis showed that, compared with the sham-operation group, the hippocampus of the model group had 50 up-regulated genes with significant difference (fold change >2), and 21 down-regulated genes with significant difference (fold change <0.5); compared with the hippocampus of the model group, the hippocampus of the Tiantai No. 1 group was found to have 5 up-regulated genes with significant difference (fold change >2) and 20 down-regulated genes with significant difference (fold change <0.5). The functions of differentially expressed genes of the groups were involved in nervous system's development, neuronic differentiation and function-regulation, cellular growth and differentiation and apoptosis, synaptic occurrence and plasticity, inflammation and immune response, ion channels/transporters, cellular signal transduction, cellular material/energy metabolism and so on.

CONCLUSION

Tiantai No. 1 can regulate hippocampal function, and further regulate the brain function of animals in multiple gene target points by a number of ways.

Luteolin modulates 6-hydroxydopamine-induced transcriptional changes of stress response pathways in PC12 cells

The neurotoxin 6-hydroxydopamine (6-OHDA), which causes transcriptional changes associated with oxidative and proteotoxic stress, has been widely used to generate an experimental model of Parkinson's disease. The food-derived compound luteolin has multi-target actions including antioxidant, anti-inflammatory and neurotrophic activities. The aim of this study is to investigate how luteolin affects 6-OHDA-mediated stress response pathways. The results showed that when PC12 cells were pre-treated with luteolin (20 µM) 30 min prior to 6-OHDA (100 µM) exposure, 6-OHDA-induced ROS overproduction, cytotoxicity, caspase-3 activation, and mRNA expression of BIM, TRB3 and GADD34 were significantly attenuated. Moreover, 6-OHDA-mediated cell cycle arrest and transcription of p53 target genes, p21, GADD45α and PUMA, were reduced by luteolin. Luteolin also significantly down-regulated 6-OHDA-mediated unfolded protein response (UPR), leading to decreases in phospho-eIF2α, ATF4, GRP78 and CHOP. In addition, luteolin attenuated 6-OHDA-induced Nrf2-mediated HO-1 and GCLC. Taken together, these results suggest that diminishing intracellular ROS formation and down-regulation of p53, UPR and Nrf2-ARE pathways may be involved in the neuroprotective effect of luteolin.

Time course of dopamine neuron loss and glial response in the 6-OHDA striatal mouse model of Parkinson's disease

The 6-hydroxydopamine (6-OHDA) neurotoxic lesion of the midbrain dopamine (DA) system is one of the most widely used techniques for modelling Parkinson's disease in rodents. The majority of studies using this approach, however, largely limit their analysis to lesioning acutely, and looking at behavioural deficits and the number of surviving tyrosine hydroxylase (TH)-stained cells in the midbrain. Here we have analysed additional characteristics that occur following intrastriatal delivery of 6-OHDA, providing better understanding of the neurodegenerative process. Female C57/Black mice were given lesions at 10 weeks old, and killed at several different time points postoperatively (3 and 6 h, 1, 3, 6, 9 and 12 days). While the detrimental effect of the toxin on the TH+ fibres in the striatum was immediate, we found that the loss of TH+ dendritic fibres, reduction in cell size and intensity of TH expression, and eventual reduction in the number of TH+ neurons in the substantia nigra was delayed for several days post-surgery. We also investigated the expression of various transcription factors and proteins expressed by midbrain DA neurons following lesioning, and observed changes in the expression of Aldh1a1 (aldehyde dehydrogenase 1 family, member A1) as the neurodegenerative process evolved. Extracellularly, we looked at microglia and astrocytes in reaction to the 6-OHDA striatal lesion, and found a delay in their response and proliferation in the substantia nigra. In summary, this work highlights aspects of the neurodegenerative process in the 6-OHDA mouse model that can be applied to future studies looking at therapeutic interventions.

The potential neuroprotection mechanism of GDNF in the 6-OHDA-induced cellular models of Parkinson's Disease

The glial cell line-derived neurotrophic factor (GDNF) potential as a therapeutic agent for the treatment of Parkinson's Disease (PD) has been extensively explored. However, the mechanism of the GDNF neuroprotective effects is still unclear. In this study, the neuroprotective mechanism of the GDNF in the PD cellular models, which was obtained by the 6-hydroxydopamine (6-OHDA)-induced dopaminergic (DA) cell line MN9D damage was investigated by microarray. Interestingly, 54 constitutively increased or decreased genes were detected, 17 of which have not been reported previously. The expression of 5 up-regulated and 5 down-regulated genes which displayed the most obvious changes compared to the no GDNF treatment cells and was previously proven to be related to cell survival was validated by real-time PCR and western blot. Moreover, the up-regulated gene Ager and down-regulated gene Ccnl2 which were related to the PI-3K/Akt signaling pathway, but not researched in the neuron-cells, were investigated by overexpression and RNA interference. Overexpression of Ager or knockdown the expression of Ccnl2 decreased the damage to MN9D cells caused by 6-OHDA and reduced their apoptosis. All these results suggested that the protective effects of the GDNF on the 6-OHDA damaged MN9D cells could be understood by enhancing the expression of the apoptosis inhibiting genes and decreasing the expression of the apoptosis promoting genes. Thus, this study might provide a number of specific candidates and potential targets to investigate the protective mechanism of GDNF in DA neurons.

Effects of glial cell line-derived neurotrophic factor on microRNA expression in a 6-hydroxydopamine-injured dopaminergic cell line

Parkinson's disease (PD) is the second most prevalent, progressive neurodegenerative disease and is characterized by the irreversible and selective loss of nigrostriatal dopaminergic (DA) neurons. Glial cell line-derived neurotrophic factor (GDNF), which is a potent protective factor for DA neurons, is considered a promising neuroprotective candidate for PD. microRNAs (miRNAs) have been shown to be involved in a number of neurodegenerative diseases. Both miRNAs and GDNF affect DA neuronal processes, but the molecular crosstalk between these molecules remains unclear. The present study aimed to evaluate whether GDNF modulates miRNA expression. We used microarray analysis and real-time polymerase chain reaction (RT-PCR) to investigate miRNAs expression in 6-hydroxydopamine (6-OHDA)-injured MN9D cells treated with GDNF for 30 min, 1 h, or 3 h. Our results showed that GDNF treatment led to differential expression of 143 miRNAs. To further identify mechanisms by which GDNF exerts its effects, we compared miRNAs and mRNAs microarray data at the 1-h time point. We found that various biological processes and pathways were regulated at the miRNA level following GDNF treatment. Collectively, these results provide evidence of the capacity of GDNF to influence miRNAs expression, suggesting a new mechanism of GDNF action.

Sequences located within the N-terminus of the PD-linked LRRK2 lead to increased aggregation and attenuation of 6-hydroxydopamine-induced cell death

Clinical symptoms of Parkinson's disease (PD) arise from the loss of substantia nigra neurons resulting in bradykinesia, rigidity, and tremor. Intracellular protein aggregates are a pathological hallmark of PD, but whether aggregates contribute to disease progression or represent a protective mechanism remains unknown. Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene have been linked to PD in both familial cases and idiopathic cases and aggregates of the LRRK2 protein are present in postmortem PD brain samples. To determine whether LRRK2 contains a region of protein responsible for self-aggregation, two independent, bioinformatic algorithms were used to identify an N-terminal amino acid sequence as being aggregation-prone. Cells subsequently transfected with a construct containing this domain were found to have significantly increased protein aggregation compared to wild type protein or a construct containing only the last half of the molecule. Finally, in support of the hypothesis that aggregates represent a self-protection strategy, aggregated N-terminal LRRK2 constructs significantly attenuated cell death induced by the PD-mimetic, 6-hydroxydopamine (6-OHDA).

Programmed cell death in Parkinson's disease

Parkinson's disease is a debilitating disorder characterized by a progressive loss of dopaminergic neurons caused by programmed cell death. The aim of this review is to provide an up-to-date summary of the major programmed cell death pathways as they relate to PD. For a long time, programmed cell death has been synonymous with apoptosis but there now is evidence that other types of programmed cell death exist, such as autophagic cell death or programmed necrosis, and that these types of cell death are relevant to PD. The pathways and signals covered here include namely the death receptors, BCL-2 family, caspases, calpains, cdk5, p53, PARP-1, autophagy, mitophagy, mitochondrial fragmentation, and parthanatos. The review will present evidence from postmortem PD studies, toxin-induced models (especially MPTP/MPP+, 6-hydroxydopamine and rotenone), and from α-synuclein, LRRK2, Parkin, DJ-1, and PINK1 genetic models of PD, both in vitro and in vivo.

Microarray expression profiling in 6-hydroxydopamine-induced dopaminergic neuronal cell death

Parkinson's disease (PD) is the second most common neurodegenerative disorder and is characterized by a loss of dopaminergic neurons in the substantia nigra pars compacta. To discover potential key molecules in this process, we utilized cDNA microarray technology to obtain an expression profile of transcripts in MN9D dopaminergic neuronal cells treated with 6-hydroxydopamine. Using a self-organizing map algorithm, data mining and clustering were combined to identify distinct functional subgroups of genes. We identified alterations in the expression of 81 genes in eight clusters. Among these genes, we verified protein expression patterns of MAP kinase phosphatase 1 and sequestosome 1 using both cell culture and rat brain models of PD. Immunological analyses revealed increased expression levels as well as aggregated distribution patterns of these gene products in 6-hydroxydopamine-treated dopaminergic neurons. In addition to the identification of other proteins that are known to be associated with protein aggregation, our results raise the possibility that a more widespread set of proteins may be associated with the generation of protein aggregates in dying neurons. Further research to determine the functional roles of other altered gene products within the same cluster as well as the seven remaining clusters may provide new insights into the neurodegeneration that underlies PD pathogenesis.

6-OHDA generated ROS induces DNA damage and p53- and PUMA-dependent cell death

BACKGROUND

Parkinson's disease (PD) is characterized by the selective loss of dopaminergic neurons in the substantia nigra (SN), resulting in tremor, rigidity, and bradykinesia. Although the etiology is unknown, insight into the disease process comes from the dopamine (DA) derivative, 6-hydroxydopamine (6-OHDA), which produces PD-like symptoms. Studies show that 6-OHDA activates stress pathways, such as the unfolded protein response (UPR), triggers mitochondrial release of cytochrome-c, and activates caspases, such as caspase-3. Because the BH3-only protein, Puma (p53-upregulated mediator of apoptosis), is activated in response to UPR, it is thought to be a link between cell stress and apoptosis.

RESULTS

To test the hypothesis that Puma serves such a role in 6-OHDA-mediated cell death, we compared the response of dopaminergic neurons from wild-type and Puma-null mice to 6-OHDA. Results indicate that Puma is required for 6-OHDA-induced cell death, in primary dissociated midbrain cultures as well as in vivo. In these cultures, 6-OHDA-induced DNA damage and p53 were required for 6-OHDA-induced cell death. In contrast, while 6-OHDA led to upregulation of UPR markers, loss of ATF3 did not protect against 6-OHDA.

CONCLUSIONS

Together, our results indicate that 6-OHDA-induced upregulation of Puma and cell death are independent of UPR. Instead, p53 and DNA damage repair pathways mediate 6-OHDA-induced toxicity.

Novel CDNF/MANF family of neurotrophic factors

Current therapeutic interventions for neurodegenerative diseases alleviate only disease symptoms, while treatments that could stop or reverse actual degenerative processes are not available. Parkinson's disease (PD) is a movement disorder with characteristic degeneration of dopaminergic neurons in the midbrain. Few neurotrophic factors (NTFs) that promote survival, maintenance, and differentiation of affected brain neurons are considered as potential therapeutic agents for the treatment of neurodegenerative diseases. Thus, it is important to search and study new NTFs that could also be used in therapy. In this review, we discuss novel evolutionary conserved family of NTFs consisting of two members in the vertebrates, cerebral dopamine neurotrophic factor (CDNF) and mesencephalic astrocyte-derived neurotrophic factor (MANF). Invertebrates, including Drosophila and Caenorhabditis have a single protein homologous to vertebrate CDNF/MANF. Characteristic feature of these proteins is eight structurally conserved cysteine residues, which determine the protein fold. The crystal structure analysis revealed that CDNF and MANF consist of two domains; an amino-terminal saposin-like domain that may interact with lipids or membranes, and a presumably unfolded carboxy-terminal domain that may protect cells against endoplasmic reticulum stress. CDNF and MANF protect midbrain dopaminergic neurons and restore motor function in 6-hydroxydopamine rat model of PD in vivo. In line, Drosophila MANF is needed for the maintenance of dopaminergic neurites and dopamine levels in the fly, suggesting that the function of CDNF/MANF proteins is evolutionary conserved. Future studies will reveal the receptors and mode of action of these novel factors, which are potential therapeutic proteins for the treatment of PD.

Toxicogenomics: transcription profiling for toxicology assessment

Toxicogenomics, the application of transcription profiling to toxicology, has been widely used for elucidating the molecular and cellular actions of chemicals and other environmental stressors on biological systems, predicting toxicity before any functional damages, and classification of known or new toxicants based on signatures of gene expression. The success of a toxicogenomics study depends upon close collaboration among experts in different fields, including a toxicologist or biologist, a bioinformatician, statistician, physician and, sometimes, mathematician. This review is focused on toxicogenomics studies, including transcription profiling technology, experimental design, significant gene extraction, toxicological results interpretation, potential pathway identification, database input and the applications of toxicogenomics in various fields of toxicological study.

Cell stress induced by the parkinsonian mimetic, 6-hydroxydopamine, is concurrent with oxidation of the chaperone, ERp57, and aggresome formation

Parkinson's disease (PD) involves an irreversible degeneration of the nigrostriatal pathway. As most cases of PD are sporadic, environmental risk factors may underlie neurodegeneration in dopaminergic neurons. One such factor is 6-hydroxydopamine (6-OHDA), which is widely used as a parkinsonian mimetic. Studies have shown that 6-OHDA generates reactive oxygen species and induces cell stress, the unfolded protein response, and apoptosis. Present findings show that 6-OHDA, but not hydrogen peroxide, MPP+, or rotenone, leads to the rapid formation of high-molecular-weight species of protein disulfide isomerase-associated protein 3 (ERp57) in a dose- and time-dependent fashion. Moreover, ERp57 conjugates are blocked by N-acetylcysteine and glutathione, suggesting that they represent oxidized forms of protein. Surprisingly, conjugates are complexed with DNA, because treatment with DNase reduces their appearance. Subcellular fractionation indicates that both nuclear and mitochondrial DNA are associated with the protein. Finally, toxin-treated ERp57 rapidly forms juxtanuclear aggresome-like structures in dopaminergic cells, suggesting that ERp57 plays an early adaptive response in toxin-mediated stress. Understanding the signaling mechanisms associated with parkinsonian mimetics, as well as their temporal induction, may aid in designing better interventions in models of PD.

Oxidative stress-triggered unfolded protein response is upstream of intrinsic cell death evoked by parkinsonian mimetics

Oxidative stress is a key player in a variety of neurodegenerative disorders including Parkinson's disease. Widely used as a parkinsonian mimetic, 6-hydroxydopamine (6-OHDA) generates reactive oxygen species (ROS) as well as coordinated changes in gene transcription associated with the unfolded protein response (UPR) and apoptosis. Whether 6-OHDA-induced UPR activation is dependent on ROS has not yet been determined. The present study used molecular indicators of oxidative stress to place 6-OHDA-generated ROS upstream of the appearance of UPR markers such as activating transcription factor 3 (ATF3) and phosphorylated stress-activated protein kinase (SAPK/JNK) signaling molecules. Antioxidants completely blocked 6-OHDA-mediated UPR activation and rescued cells from toxicity. Moreover, cytochrome c release from mitochondria was observed after the appearance of early UPR markers, suggesting that cellular stress pathways are responsible for its release. Mechanistically, the 6-OHDA-induced UPR was independent of intracellular calcium changes. Rather, evidence of protein oxidation was observed before the expression of UPR markers, suggesting that the rapid accumulation of damaged proteins triggered cell stress/UPR. Taken together, 6-OHDA-mediated cell death in dopaminergic cells proceeds via ROS-dependent UPR up-regulation which leads to an interaction with the intrinsic mitochondrial pathway and downstream caspase activation.