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Dysregulated expression and alternative splicing of genes controlling neuritogenesis and axon guidance revealed by exon-sensitive microarrays in models of neurodegeneration

ABSTRACT: Mitochondrial dysfunction has been directly or indirectly implicated in the pathogenesis of a number of neurodegenerative disorders including Parkinson's disease, Alzheimer's disease and Amyotrophic Lateral Sclerosis (ALS). We used exon-sentive microarrays to characterize the responses to different mitochondrial perturbations in cellular models. We examined human SH-SY5Y neuroblastoma cells treated with paraquat, a neurotoxic herbicide which both catalyzes the formation of reactive oxygen species (ROS) and induces mitochondrial damage in animal models, and SH-SY5Y cells stably expressing the mutant SOD1(G93A) protein, one of the genetic causes of ALS. We identified a common set of genes that have a deregulated transcription and alternative splicing in both models. Noticeably, pathway analysis revealed that the expression of a subset of genes involved in neuritogenesis and axon guidance is perturbed, suggesting that alterations of axonal function may descend directly from mitochondrial damage and be responsible for neurodegenerative conditions. This SuperSeries is composed of the SubSeries listed below.

ORGANISM(S): Homo sapiens

PROVIDER: GSE21450 | GEO | 2010/12/22

SECONDARY ACCESSION(S): PRJNA126051

REPOSITORIES: GEO

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Project description:This SuperSeries is composed of the following subset Series: GSE21298: Profiling wt SOD versus ALS SOD1(G93A) mutant GSE21305: Profiling neuroblastoma SH-SY5Y with Paraquat treatment Mitochondrial dysfunction has been directly or indirectly implicated in the pathogenesis of a number of neurodegenerative disorders including Parkinson's disease, Alzheimer's disease and Amyotrophic Lateral Sclerosis (ALS). We used exon-sentive microarrays to characterize the responses to different mitochondrial perturbations in cellular models. We examined human SH-SY5Y neuroblastoma cells treated with paraquat, a neurotoxic herbicide which both catalyzes the formation of reactive oxygen species (ROS) and induces mitochondrial damage in animal models, and SH-SY5Y cells stably expressing the mutant SOD1(G93A) protein, one of the genetic causes of ALS. We identified a common set of genes that have a deregulated transcription and alternative splicing in both models. Noticeably, pathway analysis revealed that the expression of a subset of genes involved in neuritogenesis and axon guidance is perturbed, suggesting that alterations of axonal function may descend directly from mitochondrial damage and be responsible for neurodegenerative conditions. Paraquat treatment on cell lines derived from human neuroblastoma SH-SY5Y and the same cell line stably transfected with cDNAs coding for wild type SOD1 or ALS mutant SOD1 G93A was carried out as described in (Maracchioni et al. J Neurochem 2007, 100, 142-153). Human neuroblastoma SH-SY5Y untransfected or stably transfected with cDNAs coding for wild type SOD1 or the mutant SOD1(G93A) , were cultured in D-MEM/F-12 media with GlutaMAX™ (Gibco, Invitrogen, UK), 10% FBS, 100 Units/ml penicillin G, 100µg/ml streptomycin/ penicillin (Euroclone, Milano, Italy). Stably transfected cells were also maintained in the presence of 400µg/ml Geneticin (G418 sulphate, Euroclone). Cells were fed every 2–3 days and passed once a week. For the microarray experiment, after an initial amplification of each cell type [(SH-SY5Y; SOD1(WT), SOD1(G93A)], cells were aliquoted and cryopreservated in liquid nitrogen. For every experiment an aliquot of each cell line was thawed and seeded. After having reached confluence, cells were reseeded at 3x106cells in 100mm dish. Paraquat (N,N’-dimethyl-4,4’-bipyridinium dichloride, Sigma-Aldrich) treatment was carried out as described in (Maracchioni et al. J Neurochem 2007, 100, 142-153). Total RNA was extracted using TRIzol® Reagent (Invitrogen), and subsequently purified using silica membrane spin columns from RNeasy Mini kit (Qiagen). RNA quantity and purity were assessed using a NanoDrop® instrument (Thermo Fisher Scientific Inc.). Total RNA integrity was assessed by using a 2100 Bioanalyzer (Agilent Technologies) and the RNA Integrity Number (RIN) was calculated. Each condition was replicated 5 times. After extraction and quality check 1.5 µg of total RNA was subjected to removal of ribosomal RNA following the procedure suggested by the manufacturer (Affymetrix). The resulting total RNA was then used to created the biotin-labeled library to be hybridized on GeneChip® Exon 1.0 ST human microarrays following the procedure described by the manufacturer (Affymetrix). The CEL files resulting from the hybridization were analyzed using oneChannelGUI 1.6.5 (Sanges et al. Bioinformatics 2007, 23, 3406-3408). Exon and gene-level probeset summarization was done by mean of RMA and sketch quantile normalization. Gene-level differential expression: to assess differential expression at gene-level, we used an empirical Bayes method together with a false discovery rate (FDR) correction of the p-value Thus, the list of differentially expressed genes was generated using an FDR ≤ 0.05 together with an absolute log2(fold-change) threshold of 1. Exon-level analysis: an intensity filter was subsequently applied at gene-level to remove not expressed and low expressed genes, i.e. genes were retained for exon-level analysis if in all biological replication gene-level signal was greater than 5. Subsequently, only genes characterized to have at least two RNA isoforms annotated in Ensembl database were retained for further analysis. The Splicing Index value was calculated by taking the log2 ratio of the normalized exon intensity (NI) in Sample 1 and the NI in Sample 2. The normalized exon intensity (NI) is the ratio of the probe set intensity to the gene intensity. Alternative splicing events (ASEs) were detected as described in (Della Beffa et al. BMC Genomics 2008, 9, 571).

Project description:Amyotrophic lateral sclerosis (ALS) is a deleterious neurodegenerative disease without effective treatment options. Recent studies have indicated the involvement of the dysregulation of RNA metabolism in the pathogenesis of ALS. Among the various RNA regulatory machineries, nonsense-mediated mRNA decay (NMD) is a stress responsive cellular surveillance system that degrades selected mRNA substrates to prevent the translation of defective or harmful proteins. Whether this pathway is affected in neurodegenerative diseases is unclear. Here we report that the NMD pathway is inhibited in ALS patients with C9orf72 hexanucleotide repeat expansion (HRE), the most common cause of familial ALS. Bioinformatic analysis of multiple transcriptome profiles revealed significant overlap of upregulated genes in NMD-defective cells with those in the brain tissues, micro-dissected motor neurons, or induced pluripotent stem cell-derived motor neurons from ALS patients carrying C9orf72 HRE, suggesting the suppression of NMD pathway in these patients. In contrast, there are few overlapping upregulated genes in brain tissues from sporadic ALS patients with those in NMD-defective cells. Using Drosophila models expressing various C9orf72 HRE products, we have validated the suppression of the NMD pathway by C9orf72 HRE and identified arginine-rich dipeptide repeats (DPRs) generated from HRE as the main culprits of NMD inhibition. Furthermore, in human SH-SY5Y neuroblastoma cells and in mouse brains, expression of arginine-rich DPRs was sufficient to cause NMD inhibition. Remarkably, expression of UPF1, a core gene in the NMD pathway, efficiently blocked neurotoxicity caused by arginine-rich DPRs in both cellular and Drosophila models. Although not as effective as UPF1, expression of another NMD gene UPF2 also ameliorated the degenerative phenotypes in DPR-expressing flies, indicating neuroprotection by genetically reactivating the NMD pathway. Finally, after validating Tranilast as an NMD-activating drug, we demonstrated its therapeutic potential in cellular and Drosophila models of C9orf72 DPR neurotoxicity. Therefore, our study has revealed the suppression of NMD in C9orf72 ALS and has suggested that the restoration of the NMD pathway by Tranilast, an asthma drug with solid safety record, could be a promising therapeutic strategy for ALS.

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Dysregulated expression and alternative splicing of genes controlling neuritogenesis and axon guidance revealed by exon-sensitive microarrays in models of neurodegeneration

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