Background: Although the global use of the endocrine-disrupting chemical DDT has decreased, its persistence in the environment has resulted in continued human exposure. Accumulating evidence suggests that DDT exposure has long-term adverse effects on development, yet the impact on growth and differentiation of adult stem cells remains unclear.
Objectives: Human mesenchymal stem cells (MSCs) exposed to DDT were used to evaluate the impact on stem cell biology.
Methods: We assessed DDT-treated MSCs for self-renewal, proliferation, and differentiation potential. Whole genome RNA sequencing was performed to assess gene expression in DDT-treated MSCs.
Results: MSCs exposed to DDT formed fewer colonies, suggesting a reduction in self-renewal potential. DDT enhanced both adipogenic and osteogenic differentiation, which was confirmed by increased mRNA expression of glucose transporter type 4 (GLUT4), lipoprotein lipase (LpL), peroxisome proliferator-activated receptor gamma (PPARγ), leptin, osteonectin, core binding factor 1 (CBFA1), and FBJ murine osteosarcoma viral oncogene homolog (c-Fos). Expression of factors in DDT-treated cells was similar to that in estrogen-treated MSCs, suggesting that DDT may function via the estrogen receptor (ER)-mediated pathway. The coadministration of ICI 182,780 blocked the effects of DDT. RNA sequencing revealed 121 genes and noncoding RNAs to be differentially expressed in DDT-treated MSCs compared with controls cells.
Conclusion: Human MSCs provide a powerful biological system to investigate and identify the molecular mechanisms underlying the effects of environmental agents on stem cells and human health. MSCs exposed to DDT demonstrated profound alterations in self-renewal, proliferation, differentiation, and gene expression, which may partially explain the homeostatic imbalance and increased cancer incidence among those exposed to long-term EDCs.
Citation: Strong AL, Shi Z, Strong MJ, Miller DF, Rusch DB, Buechlein AM, Flemington EK, McLachlan JA, Nephew KP, Burow ME, Bunnell BA. 2015. Effects of the endocrine-disrupting chemical DDT on self-renewal and differentiation of human mesenchymal stem cells. Environ Health Perspect 123:42–48; http://dx.doi.org/10.1289/ehp.1408188
The high level of accuracy and sensitivity of next generation sequencing for quantifying genetic material across organismal boundaries gives it tremendous potential for pathogen discovery and diagnosis in human disease. Despite this promise, substantial bacterial contamination is routinely found in existing human-derived RNA-seq datasets that likely arises from environmental sources. This raises the need for stringent sequencing and analysis protocols for studies investigating sequence-based microbial signatures in clinical samples.
Hexanucleotide repeat expansions in chromosome 9 open reading frame 72 (C9ORF72) are causative for frontotemporal dementia (FTD) and motor neuron disease (MND). Substantial phenotypic heterogeneity has been described in patients with these expansions. We set out to identify genetic modifiers of disease risk, age at onset, and survival after onset that may contribute to this clinical variability.
We examined a cohort of 330 C9ORF72 expansion carriers and 374 controls. In these individuals, we assessed variants previously implicated in FTD and/or MND; 36 variants were included in our analysis. After adjustment for multiple testing, our analysis revealed three variants significantly associated with age at onset (rs7018487 [UBAP1; p-value = 0.003], rs6052771 [PRNP; p-value = 0.003], and rs7403881 [MT-Ie; p-value = 0.003]), and six variants significantly associated with survival after onset (rs5848 [GRN; p-value = 0.001], rs7403881 [MT-Ie; p-value = 0.001], rs13268953 [ELP3; p-value = 0.003], the epsilon 4 allele [APOE; p-value = 0.004], rs12608932 [UNC13A; p-value = 0.003], and rs1800435 [ALAD; p-value = 0.003]).
Variants identified through this study were previously reported to be involved in FTD and/or MND, but we are the first to describe their effects as potential disease modifiers in the presence of a clear pathogenic mutation (i.e. C9ORF72 repeat expansion). Although validation of our findings is necessary, these variants highlight the importance of protein degradation, antioxidant defense and RNA-processing pathways, and additionally, they are promising targets for the development of therapeutic strategies and prognostic tests.
Electronic supplementary material
The online version of this article (doi:10.1186/1750-1326-9-38) contains supplementary material, which is available to authorized users.
C9ORF72; Frontotemporal dementia; Motor neuron disease; Genetic modifier; Repeat expansion
MicroRNAs (miRNAs) are small non-coding RNAs that regulate the majority of the transcriptome at a post-transcriptional level. Because of this critical role, it is important to ensure that the assays used to determine their functionality are robust and reproducible. Typically, the reporter gene assay in cell-based systems has been the first-line method to study miRNA functionality. In order to overcome some of the potential errors in interpretation that can be associated with this assay, we have developed a detailed protocol for the luciferase reporter gene assay that has been modified for miRNAs. We demonstrate that normalization against the effect of the miRNA and cellular factors on the luciferase coding sequence is essential to obtain the specific impact of the miRNA on the 3'UTR (untranslated region) target. Our findings suggest that there is a real possibility that the roles for miRNA in transcriptome regulation may be misreported due to inaccurate normalization of experimental data and also that up-regulatory effects of miRNAs are not uncommon in cells. We propose to establish this comprehensive method as standard for miRNA luciferase reporter assays to avoid errors and misinterpretations in the functionality of miRNAs.
reporter gene assay; miRNA; normalization; NEFL (neurofilament)
Small GTPases participate in a broad range of cellular processes such as proliferation, differentiation, and migration. The exchange of GDP for GTP resulting in the activation of these GTPases is catalyzed by a group of enzymes called guanine nucleotide exchange factors (GEFs), of which two classes: Dbl-related exchange factors and the more recently described dedicator of cytokinesis proteins family exchange factors. Increasingly, deregulation of normal GEF activity or function has been associated with a broad range of disease states, including neurodegeneration and neurodevelopmental disorders. In this review, we examine this evidence with special emphasis on the novel role of Rho guanine nucleotide exchange factor (RGNEF/p190RhoGEF) in the pathogenesis of amyotrophic lateral sclerosis. RGNEF is the first neurodegeneration-linked GEF that regulates not only RhoA GTPase activation but also functions as an RNA binding protein that directly acts with low molecular weight neurofilament mRNA 3′ untranslated region to regulate its stability. This dual role for RGNEF, coupled with the increasing understanding of the key role for GEFs in modulating the GTPase function in cell survival suggests a prominent role for GEFs in mediating a critical balance between cytotoxicity and neuroprotection which, when disturbed, contributes to neuronal loss.
neurofilament; RNA binding proteins; GEF; neurodegeneration; motor neuron disease
Epstein-Barr virus (EBV) reactivation involves the ordered induction of approximately 90 viral genes that participate in the generation of infectious virions. Using strand-specific RNA-seq to assess the EBV transcriptome during reactivation, we found extensive bidirectional transcription extending across nearly the entire genome. In contrast, only 4% of the EBV genome is currently bidirectionally annotated. Most of the newly identified transcribed regions show little evidence of coding potential, supporting noncoding roles for most of these RNAs. Based on previous cellular long noncoding RNA size calculations, we estimate that there are likely hundreds more EBV genes expressed during reactivation than was previously known. Limited 5′ and 3′ rapid amplification of cDNA ends (RACE) experiments and findings of novel splicing events by RNA-seq suggest that the complexity of the viral genome during reactivation may be even greater. Further analysis of antisense transcripts at some of the EBV latency gene loci showed that they are “late” genes, they are nuclear, and they tend to localize in areas of the nucleus where others find newly synthesized viral genomes. This raises the possibility that these transcripts perform functions such as new genome processing, stabilization, organization, etc. The finding of a significantly more complex EBV transcriptome during reactivation changes our view of the viral production process from one that is facilitated and regulated almost entirely by previously identified viral proteins to a process that also involves the contribution of a wide array of virus encoded noncoding RNAs.
Comprehensive virome analysis of RNA sequence (RNA-seq) data sets from 118 non-Hodgkin's B-cell lymphomas revealed a small subset that is positive for Epstein-Barr virus (EBV) or human herpesvirus 6B (HHV-6B), with one coinfection. EBV transcriptome analysis revealed expression of the latency genes RPMS1, LMP1, and LMP2, with one sample additionally showing a high level of early lytic expression and another sample showing a high level of EBNA2 expression. HHV-6B transcriptome analysis revealed that the majority of genes were transcribed.
High-throughput RNA sequencing (RNA-seq) has become an instrumental assay for the analysis of multiple aspects of an organism's transcriptome. Further, the analysis of a biological specimen's associated microbiome can also be performed using RNA-seq data and this application is gaining interest in the scientific community. There are many existing bioinformatics tools designed for analysis and visualization of transcriptome data. Despite the availability of an array of next generation sequencing (NGS) analysis tools, the analysis of RNA-seq data sets poses a challenge for many biomedical researchers who are not familiar with command-line tools. Here we present RNA CoMPASS, a comprehensive RNA-seq analysis pipeline for the simultaneous analysis of transcriptomes and metatranscriptomes from diverse biological specimens. RNA CoMPASS leverages existing tools and parallel computing technology to facilitate the analysis of even very large datasets. RNA CoMPASS has a web-based graphical user interface with intrinsic queuing to control a distributed computational pipeline. RNA CoMPASS was evaluated by analyzing RNA-seq data sets from 45 B-cell samples. Twenty-two of these samples were derived from lymphoblastoid cell lines (LCLs) generated by the infection of naïve B-cells with the Epstein Barr virus (EBV), while another 23 samples were derived from Burkitt's lymphomas (BL), some of which arose in part through infection with EBV. Appropriately, RNA CoMPASS identified EBV in all LCLs and in a fraction of the BLs. Cluster analysis of the human transcriptome component of the RNA CoMPASS output clearly separated the BLs (which have a germinal center-like phenotype) from the LCLs (which have a blast-like phenotype) with evidence of activated MYC signaling and lower interferon and NF-kB signaling in the BLs. Together, this analysis illustrates the utility of RNA CoMPASS in the simultaneous analysis of transcriptome and metatranscriptome data. RNA CoMPASS is freely available at http://rnacompass.sourceforge.net/.
Amyotrophic lateral sclerosis (ALS) is the most common motor neuron diseases (MND), while frontotemporal lobar degeneration (FTLD) is the second most common cause of early-onset dementia. Many ALS families segregating FTLD have been reported, particularly over the last decade. Recently, mutations in TARDBP, FUS/TLS, and C9ORF72 have been identified in both ALS and FTLD patients, while mutations in VCP, a FTLD associated gene, have been found in ALS families. Distinct variants located in the 3′-untranslated region (UTR) of the SIGMAR1 gene were previously reported in three unrelated FTLD or FTLD–MND families. We directly sequenced the coding and UTR regions of the SIGMAR1 gene in a targeted cohort of 25 individual familial ALS cases of Caucasian origin with a history of cognitive impairments. This screening identified one variant in the 3′-UTR of the SIGMAR1 gene in one ALS patient, but the same variant was also observed in 1 out of 380 control chromosomes. Subsequently, we screened the same samples for a C9ORF72 repeat expansion: 52% of this cohort was found expanded, including the sample with the SIGMAR1 3′-UTR variant. Consequently, coding and noncoding variants located in the 3′-UTR region of the SIGMAR1 gene are not the cause of FTLD–MND in our cohort, and more than half of this targeted cohort is genetically explained by C9ORF72 repeat expansions.
amyotrophic lateral sclerosis; frontotemporal lobar degeneration; motor neuron disease; dementia
Amyotrophic lateral sclerosis (ALS) is a fatal disease characterized by progressive motor neuron degeneration and neurofilament aggregate formation. Spinal motor neurons in ALS also show a selective suppression in the levels of low molecular weight neurofilament (NEFL) mRNA. We have been interested in investigating the role of microRNAs (miRNAs) in NEFL transcript stability. MiRNAs are small, 20–25 nucleotide, non-coding RNAs that act as post-transcriptional gene regulators by targeting the 3′ untranslated region (3′UTR) of mRNA resulting in mRNA decay or translational silencing. In this study, we characterized putative novel miRNAs from a small RNA library derived from control and sporadic ALS (sALS) spinal cords. We detected 80 putative novel miRNAs, 24 of which have miRNA response elements (MREs) within the NEFL mRNA 3′UTR. From this group, we determined by real-time PCR that 10 miRNAs were differentially expressed in sALS compared to controls. Functional analysis by reporter gene assay and relative quantitative RT-PCR showed that two novel miRNAs, miR-b1336 and miR-b2403, were downregulated in ALS spinal cord and that both stabilize NEFL mRNA. We confirmed the direct effect of these latter miRNAs using anit-miR-b1336 and anti-miR-b2403. These results demonstrate that the expression of two miRNAs (miRNAs miR-b1336 and miR-b2403) whose effect is to stabilize NEFL mRNA are down regulated in ALS, the net effect of which is predicted to contribute directly to the loss of NEFL steady state mRNA which is pathognomic of spinal motor neurons in ALS.
Expansions of the non-coding GGGGCC hexanucleotide repeat in the chromosome 9 open reading frame 72 (C9ORF72) gene were recently identified as the long sought-after cause of frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) on chromosome 9p. In this study we aimed to determine whether the length of the normal - unexpanded - allele of the GGGGCC repeat in C9ORF72 plays a role in the presentation of disease or affects age at onset in C9ORF72 mutation carriers. We also studied whether the GGGGCC repeat length confers risk or affects age at onset in FTD and ALS patients without C9ORF72 repeat expansions. C9ORF72 genotyping was performed in 580 FTD, 995 ALS and 160 FTD-ALS patients and 1444 controls, leading to the identification of 211 patients with pathogenic C9ORF72 repeat expansions and an accurate quantification of the length of the normal alleles in all patients and controls. No meaningful association between the repeat length of the normal alleles of the GGGGCC repeat in C9ORF72 and disease phenotype or age at onset was observed in C9ORF72 mutation carriers or non-mutation carriers.
Amyotrophic lateral sclerosis; Frontotemporal Dementia; C9ORF72; Repeat-expansion disease; Association study
Using a simple viral genome enrichment approach, we report the de novo assembly of the Akata and Mutu Epstein-Barr virus (EBV) genomes from a single lane of next-generation sequencing (NGS) reads. The Akata and Mutu viral genomes are type I EBV strains of approximately 171 kb in length. Evidence for genome heterogeneity was found for the Akata but not for the Mutu strain. A comparative analysis of Akata with another four completely sequenced EBV strains, B95-8/Raji, AG876, Mutu, and GD1, demonstrated that the Akata strain is most closely related to the GD1 strain and exhibits the greatest divergence from the type II strain, AG876. A global comparison of latent and lytic gene sequences showed that the four latency genes, EBNA2, EBNA3A, EBNA3B, and EBNA3C, are uniquely defining of type I and type II strain differences. Within type I strains, LMP1, the latency gene, is among the most divergent of all EBV genes, with three insertion or deletion loci in its CTAR2 and CTAR3 signaling domains. Analysis of the BHLF1 and LF3 genes showed that the reading frames identified in the B95-8/Raji genome are not conserved in Akata (or Mutu, for BHLF1), suggesting a primarily non-protein-coding function in EBV's life cycle. The Akata and Mutu viral-genome sequences should be a useful resource for homology-based functional prediction and for molecular studies, such as PCR, RNA-seq, recombineering, and transcriptome studies. As an illustration, we identified novel RNA-editing events in ebv-miR-BART6 antisense transcripts using the Akata and Mutu reference genomes.
Amyotrophic Lateral Sclerosis (ALS) is a progressive, adult onset, fatal neurodegenerative disease of motor neurons. There is emerging evidence that alterations in RNA metabolism may be critical in the pathogenesis of ALS. MicroRNAs (miRNAs) are small non-coding RNAs that are key determinants of mRNA stability. Considering that miRNAs are increasingly being recognized as having a role in a variety of neurodegenerative diseases, we decided to characterize the miRNA expression profile in spinal cord (SC) tissue in sporadic ALS (sALS) and controls. Furthermore, we performed functional analysis to identify a group of dysregulated miRNAs that could be responsible for the selective suppression of low molecular weight neurofilament (NFL) mRNA observed in ALS.
Using TaqMan arrays we analyzed 664 miRNAs and found that a large number of miRNAs are differentially expressed in ventral lumbar SC in sALS compared to controls. We observed that the majority of dysregulated miRNAs are down-regulated in sALS SC tissues. Ingenuity Pathway Analysis (IPA) showed that dysregulated miRNAs are linked with nervous system function and cell death. We used two prediction algorithms to develop a panel of miRNAs that have recognition elements within the human NFL mRNA 3′UTR, and then we performed functional analysis for these miRNAs. Our results demonstrate that three miRNAs that are dysregulated in sALS (miR-146a*, miR-524-5p and miR-582-3p) are capable of interacting with NFL mRNA 3′UTR in a manner that is consistent with the suppressed steady state mRNA levels observed in spinal motor neurons in ALS.
The miRNA expression profile is broadly altered in the SC in sALS. Amongst these is a group of dysregulated miRNAs directly regulate the NFL mRNA 3′UTR, suggesting a role in the selective suppression of NFL mRNA in the ALS spinal motor neuron neurofilamentous aggregate formation.
miRNA; Amyotrophic lateral sclerosis; Neurofilament
Epstein-Barr virus (EBV) is associated with roughly 10% of gastric carcinomas worldwide (EBVaGC). Although previous investigations provide a strong link between EBV and gastric carcinomas, these studies were performed using selected EBV gene probes. Using a cohort of gastric carcinoma RNA-seq data sets from The Cancer Genome Atlas (TCGA), we performed a quantitative and global assessment of EBV gene expression in gastric carcinomas and assessed EBV associated cellular pathway alterations. EBV transcripts were detected in 17% of samples but these samples varied significantly in EBV coverage depth. In four samples with the highest EBV coverage (hiEBVaGC – high EBV associated gastric carcinoma), transcripts from the BamHI A region comprised the majority of EBV reads. Expression of LMP2, and to a lesser extent, LMP1 were also observed as was evidence of abortive lytic replication. Analysis of cellular gene expression indicated significant immune cell infiltration and a predominant IFNG response in samples expressing high levels of EBV transcripts relative to samples expressing low or no EBV transcripts. Despite the apparent immune cell infiltration, high levels of the cytotoxic T-cell (CTL) and natural killer (NK) cell inhibitor, IDO1, was observed in the hiEBVaGCs samples suggesting an active tolerance inducing pathway in this subgroup. These results were confirmed in a separate cohort of 21 Vietnamese gastric carcinoma samples using qRT-PCR and on tissue samples using in situ hybridization and immunohistochemistry. Lastly, a panel of tumor suppressors and candidate oncogenes were expressed at lower levels in hiEBVaGC versus EBV-low and EBV-negative gastric cancers suggesting the direct regulation of tumor pathways by EBV.
Epstein-Barr virus (EBV) is detected in roughly 10% of gastric carcinoma (GC) cases worldwide. Despite a strong link between EBV and gastric carcinoma, the contribution of EBV to the tumor environment in EBV associated gastric carcinoma is unclear. We performed a global assessment of EBV and host cell gene expression in gastric carcinoma tumors from 71 patients to link EBV genes (and expression intensities) to cell and microenvironmental changes. In addition to the finding that EBV is associated with down-regulated tumor regulatory genes, this study revealed that samples with high levels of EBV gene expression (hiEBVaGCs) displayed elevated immune cell infiltration with high interferon-gamma (IFNG) expression compared to samples with low or no EBV gene expression. Despite this evidence of increased immune posturing, hiEBVaGC samples also showed elevated expression of the potent immune cell inhibitor, IDO1. This finding may partly explain the persistence of these virus associated tumors in the face of local immune cell concentration. Importantly, the small molecule IDO inhibitor, 1MT (1-methyl Tryptophan), has been shown to reverse the tolerance inducing effects of IDO1 in other tumors. We propose that stratification of gastric carcinomas into EBV-negative, EBV-low and EBV-high may provide indicator value for the use of IDO1 inhibitors as adjuvant therapies against hiEBVaGCs.
Respiratory muscle involvement is a recognised, but often late, complication of amyotrophic lateral sclerosis (ALS). The clinical features and prognosis of 21 patients with respiratory onset ALS are reported here. On a retrospective chart review, it was found that 2.7% of patients with ALS presenting to a tertiary care specialty clinic have respiratory symptoms as their first clinical symptom of ALS. Only 14% of these individuals presented acutely and required emergency intubation. The mean survival time of the total group from symptom onset to death or permanent ventilation was 27.0 (14.9) months, which was not significantly different from the survival time in patients with bulbar onset ALS. Non‐invasive positive pressure ventilation (NIPPV) significantly improved survival compared with those who did not use NIPPV. This study suggests that ALS with respiratory onset does not necessarily follow a rapidly progressive course.
Many cell lines commonly used for biological studies have been found to harbor exogenous agents such as the human tumor viruses Epstein-Barr virus (EBV) and human papillomavirus. Nevertheless, broad-based, unbiased approaches to globally assess the presence of ectopic organisms within cell model systems have not previously been available. We reasoned that high-throughput sequencing should provide unparalleled insights into the microbiomes of tissue culture cell systems. Here we have used our RNA-seq analysis pipeline, PARSES (Pipeline for Analysis of RNA-Seq Exogenous Sequences), to investigate the presence of ectopic organisms within two EBV-positive B-cell lines commonly used by EBV researchers. Sequencing data sets from both the Akata and JY B-cell lines were found to contain reads for EBV, and the JY data set was found to also contain reads from the murine leukemia virus (MuLV). Further investigation revealed that MuLV transcription in JY cells is highly active. We also identified a number of MuLV alternative splicing events, and we uncovered evidence of APOBEC3G (apolipoprotein B mRNA-editing enzyme, catalytic polypeptide-like 3G)-dependent DNA editing. Finally, reverse transcription-PCR analysis showed the presence of MuLV in three other human B-cell lines (DG75, Ramos, and P3HR1 Cl.13) commonly used by investigators in the Epstein-Barr virus field. We believe that a thorough examination of tissue culture microbiomes using RNA-seq/PARSES-like approaches is critical for the appropriate utilization of these systems in biological studies.
Expanded glutamine repeats of the ataxin-2 (ATXN2) protein cause spinocerebellar ataxia type 2 (SCA2), a rare neurodegenerative disorder. More recent studies have suggested that expanded ATXN2 repeats are a genetic risk factor for amyotrophic lateral sclerosis (ALS) via an RNA-dependent interaction with TDP-43. Given the phenotypic diversity observed in SCA2 patients, we set out to determine the polymorphic nature of the ATXN2 repeat length across a spectrum of neurodegenerative disorders. In this study, we genotyped the ATXN2 repeat in 3919 neurodegenerative disease patients and 4877 healthy controls and performed logistic regression analysis to determine the association of repeat length with the risk of disease. We confirmed the presence of a significantly higher number of expanded ATXN2 repeat carriers in ALS patients compared with healthy controls (OR = 5.57; P= 0.001; repeat length >30 units). Furthermore, we observed significant association of expanded ATXN2 repeats with the development of progressive supranuclear palsy (OR = 5.83; P= 0.004; repeat length >30 units). Although expanded repeat carriers were also identified in frontotemporal lobar degeneration, Alzheimer's and Parkinson's disease patients, these were not significantly more frequent than in controls. Of note, our study identified a number of healthy control individuals who harbor expanded repeat alleles (31–33 units), which suggests caution should be taken when attributing specific disease phenotypes to these repeat lengths. In conclusion, our findings confirm the role of ATXN2 as an important risk factor for ALS and support the hypothesis that expanded ATXN2 repeats may predispose to other neurodegenerative diseases, including progressive supranuclear palsy.
To discuss the epidemiology, pathogenesis, diagnosis, expected course,
prognosis, and treatment of amyotrophic lateral sclerosis (ALS), a
degenerative disorder of the nervous system associated with progressive
QUALITY OF EVIDENCE
PubMed and the Cochrane Database of Systematic Reviews were searched using
the MeSH headings “amyotrophic lateral sclerosis,” “therapy,”
“epidemiology,” and “etiology.” Articles containing the best available
evidence were reviewed. Most provided level II and III evidence. There were
some level I drug trials.
Amyotrophic lateral sclerosis is associated with progressive dysarthria,
dysphagia, and weakness in the extremities. Diagnosis is based on physical
examination, electrophysiology, and excluding other confounding conditions.
There is no cure for this devastating disorder. Certain treatments, however,
can improve survival and quality of life.
Because ALS is a complex disease, care of ALS patients is best provided at
multidisciplinary clinics that specialize in managing patients with this
Homeostatic synaptic plasticity is important for maintaining stability of neuronal function, but heterogeneous expression mechanisms suggest that distinct facets of neuronal activity may shape the manner in which compensatory synaptic changes are implemented. Here, we demonstrate that local presynaptic activity gates a retrograde form of homeostatic plasticity induced by blockade of AMPA receptors (AMPARs) in cultured hippocampal neurons. We show that AMPAR blockade produces rapid (< 3 hrs) protein synthesis-dependent increases in both presynaptic and postsynaptic function, and that the induction of presynaptic, but not postsynaptic, changes requires coincident local activity in presynaptic terminals. This “state-dependent” modulation of presynaptic function requires postsynaptic release of brain-derived neurotrophic factor (BDNF) as a retrograde messenger, which is locally synthesized in dendrites in response to AMPAR blockade. Taken together, our results reveal a local cross-talk between active presynaptic terminals and postsynaptic signaling that dictates the manner by which homeostatic plasticity is implemented at synapses.
homeostatic plasticity; retrograde signaling; BDNF; local protein synthesis; miniature neurotransmission
Amyotrophic lateral sclerosis (ALS) is a progressive and fatal motor neuron disease, and protein aggregation has been proposed as a possible pathogenetic mechanism. However, the aggregate protein constituents are poorly characterized so knowledge on the role of aggregation in pathogenesis is limited.
We carried out a proteomic analysis of the protein composition of the insoluble fraction, as a model of protein aggregates, from familial ALS (fALS) mouse model at different disease stages. We identified several proteins enriched in the detergent-insoluble fraction already at a preclinical stage, including intermediate filaments, chaperones and mitochondrial proteins. Aconitase, HSC70 and cyclophilin A were also significantly enriched in the insoluble fraction of spinal cords of ALS patients. Moreover, we found that the majority of proteins in mice and HSP90 in patients were tyrosine-nitrated. We therefore investigated the role of nitrative stress in aggregate formation in fALS-like murine motor neuron-neuroblastoma (NSC-34) cell lines. By inhibiting nitric oxide synthesis the amount of insoluble proteins, particularly aconitase, HSC70, cyclophilin A and SOD1 can be substantially reduced.
Analysis of the insoluble fractions from cellular/mouse models and human tissues revealed novel aggregation-prone proteins and suggests that nitrative stress contribute to protein aggregate formation in ALS.
To identify potential genetic modifiers contributing to the phenotypic variability that is detected in patients with repeat expansions in chromosome 9 open reading frame 72 (C9ORF72), we investigated the frequency of these expansions in a cohort of 334 subjects previously found to carry mutations in genes known to be associated with a spectrum of neurodegenerative diseases.
A 2-step protocol, with a fluorescent PCR and a repeat-primed PCR, was used to determine the presence of hexanucleotide expansions in C9ORF72. For one double mutant, we performed Southern blots to assess expansion sizes, and immunohistochemistry to characterize neuropathology.
We detected C9ORF72 repeat expansions in 4 of 334 subjects (1.2% [or 1.8% of 217 families]). All these subjects had behavioral phenotypes and also harbored well-known pathogenic mutations in either progranulin (GRN: p.C466LfsX46, p.R493X, p.C31LfsX35) or microtubule-associated protein tau (MAPT: p.P301L). Southern blotting of one double mutant with a p.C466LfsX46 GRN mutation demonstrated a long repeat expansion in brain (>3,000 repeats), and immunohistochemistry showed mixed neuropathology with characteristics of both C9ORF72 expansions and GRN mutations.
Our findings indicate that co-occurrence of 2 evidently pathogenic mutations could contribute to the pleiotropy that is detected in patients with C9ORF72 repeat expansions. These findings suggest that patients with known mutations should not be excluded from further studies, and that genetic counselors should be aware of this phenomenon when advising patients and their family members.
Middle cerebral artery occlusion (MCAo) in mice results in a brain infarct, the volume of which depends on the length of occlusion. Following permanent occlusion, neuropathological changes – including a robust glial inflammatory response – also occur downstream of the infarct in the spinal cord.
We have performed short, transient MCAo in mice to induce penumbral damage spanning the motor cortex. A 30 minute MCAo using a poly-L-lysine-coated intraluminal suture introduced through a common carotid artery incision was performed in 17 female C57BL/6 mice. Five sham-operated mice received common carotid artery ligation without insertion of the suture. Neurobehavioural assessments were performed during occlusion, immediately following reperfusion, and at 24 and 72 hours post-reperfusion. Routine histological and immunohistochemical studies were performed at 24 and 72 hours.
In 11 of the surviving 16 mice subjected to MCAo, we observed a focal, subcortical necrotic lesion and a reproducible, diffuse cortical lesion with accompanying upper motor neuron involvement. This was associated with contralateral ventral spinal cord microglial priming without significant reactive astrocytosis or lower motor neuron degeneration.
The advantages to this method are that it yields a reproducible cortical lesion, the extent of which is predictable using behavioural testing during the period of ischemia, with upper motor neuron involvement and downstream priming, but not full activation, of microglia in the lumbar spinal cord. In addition, survival is excellent following the 30 minutes of occlusion, rendering this a novel and useful model for examining the effects of microglial priming in the spinal motor neuron pool.
Under normal conditions, the proline-directed serine/threonine residues of neurofilament tail-domain repeats are exclusively phosphorylated in axons. In pathological conditions such as amyotrophic lateral sclerosis (ALS), motor neurons contain abnormal perikaryal accumulations of phosphorylated neurofilament proteins. The precise mechanisms for this compartment-specific phosphorylation of neurofilaments are not completely understood. Although localization of kinases and phosphatases is certainly implicated, another possibility involves Pin1 modulation of phosphorylation of the proline-directed serine/threonine residues. Pin1, a prolyl isomerase, selectively binds to phosphorylated proline-directed serine/threonine residues in target proteins and isomerizes cis isomers to more stable trans configurations. In this study we show that Pin1 associates with phosphorylated neurofilament-H (p-NF-H) in neurons and is colocalized in ALS-affected spinal cord neuronal inclusions. To mimic the pathology of neurodegeneration, we studied glutamate-stressed neurons that displayed increased p-NF-H in perikaryal accumulations that colocalized with Pin1 and led to cell death. Both effects were reduced upon inhibition of Pin1 activity by the use of an inhibitor juglone and down-regulating Pin1 levels through the use of Pin1 small interfering RNA. Thus, isomerization of lys-ser-pro repeat residues that are abundant in NF-H tail domains by Pin1 can regulate NF-H phosphorylation, which suggests that Pin1 inhibition may be an attractive therapeutic target to reduce pathological accumulations of p-NF-H.
Peripherin, a neuronal intermediate filament (nIF) protein found associated with pathological aggregates in motor neurons of patients with amyotrophic lateral sclerosis (ALS) and of transgenic mice overexpressing mutant superoxide dismutase-1 (SOD1G37R), induces the selective degeneration of motor neurons when overexpressed in transgenic mice. Mouse peripherin is unique compared with other nIF proteins in that three peripherin isoforms are generated by alternative splicing. Here, the properties of the peripherin splice variants Per 58, Per 56, and Per 61 have been investigated in transfected cell lines, in primary motor neurons, and in transgenic mice overexpressing peripherin or overexpressing SOD1G37R. Of the three isoforms, Per 61 proved to be distinctly neurotoxic, being assembly incompetent and inducing degeneration of motor neurons in culture. Using isoform-specific antibodies, Per 61 expression was detected in motor neurons of SOD1G37R transgenic mice but not of control or peripherin transgenic mice. The Per 61 antibody also selectively labeled motor neurons and axonal spheroids in two cases of familial ALS and immunoprecipitated a higher molecular mass peripherin species from disease tissue. This evidence suggests that expression of neurotoxic splice variants of peripherin may contribute to the neurodegenerative mechanism in ALS.
peripherin; isoforms; splicing; SOD1; ALS