BackgroundThe exact cause and mechanisms underlying the pathobiology of autism spectrum disorder (ASD) remain unclear. Dysregulation of long interspersed element-1 (LINE-1) has been reported in the brains of ASD-like mutant mice and ASD brain tissues. However, the role and methylation of LINE-1 in individuals with ASD remain unclear. In this study, we aimed to investigate whether LINE-1 insertion is associated with differentially expressed genes (DEGs) and to assess LINE-1 methylation in ASD.MethodsTo identify DEGs associated with LINE-1 in ASD, we reanalyzed previously published transcriptome profiles and overlapped them with the list of LINE-1-containing genes from the TranspoGene database. An Ingenuity Pathway Analysis (IPA) of DEGs associated with LINE-1 insertion was conducted. DNA methylation of LINE-1 was assessed via combined bisulfite restriction analysis (COBRA) of lymphoblastoid cell lines from ASD individuals and unaffected individuals, and the methylation levels were correlated with the expression levels of LINE-1 and two LINE-1-inserted DEGs, C1orf27 and ARMC8.ResultsWe found that LINE-1 insertion was significantly associated with DEGs in ASD. The IPA showed that LINE-1-inserted DEGs were associated with ASD-related mechanisms, including sex hormone receptor signaling and axon guidance signaling. Moreover, we observed that the LINE-1 methylation level was significantly reduced in lymphoblastoid cell lines from ASD individuals with severe language impairment and was inversely correlated with the transcript level. The methylation level of LINE-1 was also correlated with the expression of the LINE-1-inserted DEG C1orf27 but not ARMC8.ConclusionsIn ASD individuals with severe language impairment, LINE-1 methylation was reduced and correlated with the expression levels of LINE-1 and the LINE-1-inserted DEG C1orf27. Our findings highlight the association of LINE-1 with DEGs in ASD blood samples and warrant further investigation. The molecular mechanisms of LINE-1 and the effects of its methylation in ASD pathobiology deserve further study.

Our recent study has shown that prenatal exposure to bisphenol A (BPA) altered the expression of genes associated with autism spectrum disorder (ASD). In this study, we further investigated the effects of prenatal BPA exposure on ASD-related genes known to regulate neuronal viability, neuritogenesis, and learning/memory, and assessed these functions in the offspring of exposed pregnant rats. We found that prenatal BPA exposure increased neurite length, the number of primary neurites, and the number of neurite branches, but reduced the size of the hippocampal cell body in both sexes of the offspring. However, in utero exposure to BPA decreased the neuronal viability and the neuronal density in the hippocampus and impaired learning/memory only in the male offspring while the females were not affected. Interestingly, the expression of several ASD-related genes (e.g. Mief2, Eif3h, Cux1, and Atp8a1) in the hippocampus were dysregulated and showed a sex-specific correlation with neuronal viability, neuritogenesis, and/or learning/memory. The findings from this study suggest that prenatal BPA exposure disrupts ASD-related genes involved in neuronal viability, neuritogenesis, and learning/memory in a sex-dependent manner, and these genes may play an important role in the risk and the higher prevalence of ASD in males subjected to prenatal BPA exposure.

BackgroundAlu elements are a group of repetitive elements that can influence gene expression through CpG residues and transcription factor binding. Altered gene expression and methylation profiles have been reported in various tissues and cell lines from individuals with autism spectrum disorder (ASD). However, the role of Alu elements in ASD remains unclear. We thus investigated whether Alu elements are associated with altered gene expression profiles in ASD.MethodsWe obtained five blood-based gene expression profiles from the Gene Expression Omnibus database and human Alu-inserted gene lists from the TranspoGene database. Differentially expressed genes (DEGs) in ASD were identified from each study and overlapped with the human Alu-inserted genes. The biological functions and networks of Alu-inserted DEGs were then predicted by Ingenuity Pathway Analysis (IPA). A combined bisulfite restriction analysis of lymphoblastoid cell lines (LCLs) derived from 36 ASD and 20 sex- and age-matched unaffected individuals was performed to assess the global DNA methylation levels within Alu elements, and the Alu expression levels were determined by quantitative RT-PCR.ResultsIn ASD blood or blood-derived cells, 320 Alu-inserted genes were reproducibly differentially expressed. Biological function and pathway analysis showed that these genes were significantly associated with neurodevelopmental disorders and neurological functions involved in ASD etiology. Interestingly, estrogen receptor and androgen signaling pathways implicated in the sex bias of ASD, as well as IL-6 signaling and neuroinflammation signaling pathways, were also highlighted. Alu methylation was not significantly different between the ASD and sex- and age-matched control groups. However, significantly altered Alu methylation patterns were observed in ASD cases sub-grouped based on Autism Diagnostic Interview-Revised scores compared with matched controls. Quantitative RT-PCR analysis of Alu expression also showed significant differences between ASD subgroups. Interestingly, Alu expression was correlated with methylation status in one phenotypic ASD subgroup.ConclusionAlu methylation and expression were altered in LCLs from ASD subgroups. Our findings highlight the association of Alu elements with gene dysregulation in ASD blood samples and warrant further investigation. Moreover, the classification of ASD individuals into subgroups based on phenotypes may be beneficial and could provide insights into the still unknown etiology and the underlying mechanisms of ASD.Electronic supplementary materialThe online version of this article (10.1186/s13229-018-0213-9) contains supplementary material, which is available to authorized users.

our recent study revealed that prenatal exposure to bisphenol A (BpA) disrupted the transcriptome profiles of genes in the offspring hippocampus. In addition to genes linked to autism, several genes associated with Alzheimer's disease (AD) were found to be differentially expressed, although the association between BPA-responsive genes and AD-related genes has not been thoroughly investigated. Here, we demonstrated that in utero BpA exposure also disrupted the transcriptome profiles of genes associated with neuroinflammation and AD in the hippocampus. The level of NF-κB protein and its AD-related target gene Bace1 were significantly increased in the offspring hippocampus in a sex-dependent manner. Quantitative RT-PCR analysis also showed an increase in the expression of Tnf gene. Moreover, the reanalysis of transcriptome profiling data from several previously published BPA studies consistently showed that BPA-responsive genes were significantly associated with top AD candidate genes. The findings from this study suggest that maternal BPA exposure may increase AD risk in offspring by dysregulating genes associated with AD neuropathology and inflammation and reveal a possible relationship between AD and autism, which are linked to the same environmental factor. Sexspecific effects of prenatal BPA exposure on the susceptibility of AD deserve further investigation. Alzheimer's disease (AD) is the most common type of dementia and accounts for approximately 50-75% of dementia cases worldwide 1,2. AD is caused by progressive brain cell degeneration that affects wide areas of the cerebral cortices and hippocampi of patients, thus leading to various abnormalities, including memory loss, language difficulties, impaired decision making, and lack of other cognitive skills along with behavioral and emotional changes 3,4. Two major histological findings that are commonly found in the brain of AD patients are the (i) accumulation of extracellular amyloid plaques produced by abnormal aggregation of neurotoxic amyloid-β (Aβ) protein and (ii) intracellular neurofibrillary tangles (NFT) caused by hyperphosphorylation of tau 5,6. Amyloid plaque formation is often considered an upstream event in the pathogenesis of AD and is derived from the sequential cleavage of amyloid precursor protein (APP) by beta and gamma secretases 7. The beta-site amyloid precursor protein cleaving enzyme 1 (BACE1), which is the key enzyme responsible for APP proteolysis, initiates the cleavage

Long interspersed nucleotide element-1 (LINE-1) and Alu elements are retrotransposons whose abilities cause abnormal gene expression and genomic instability. Several studies have focused on DNA methylation profiling of gene regions, but the locus-specific methylation of LINE-1 and Alu elements has not been identified in autism spectrum disorder (ASD). Here we interrogated locus- and family-specific methylation profiles of LINE-1 and Alu elements in ASD whole blood using publicly-available Illumina Infinium 450 K methylation datasets from heterogeneous ASD and ASD variants (Chromodomain Helicase DNA-binding 8 (CHD8) and 16p11.2del). Total DNA methylation of repetitive elements were notably hypomethylated exclusively in ASD with CHD8 variants. Methylation alteration in a family-specific manner including L1P, L1H, HAL, AluJ, and AluS families were observed in the heterogeneous ASD and ASD with CHD8 variants. Moreover, LINE-1 and Alu methylation within target genes is inversely related to the expression level in each ASD variant. The DNA methylation signatures of the LINE-1 and Alu elements in ASD whole blood, as well as their associations with the expression of ASD-related genes, have been identified. If confirmed in future larger studies, these findings may contribute to the identification of epigenomic biomarkers of ASD.

BackgroundLong interspersed nucleotide element-1 (LINE-1) and Alu elements are retrotransposons whose abilities cause abnormal gene expression and genomic instability. Several studies have focused on DNA methylation profiling of gene regions, but the locus-specific methylation of LINE-1 and Alu elements has not been identified in autism spectrum disorder (ASD). MethodsDNA methylation age was predicted using Horvath’s method. We interrogated locus- and family-specific methylation profiles of LINE-1 and Alu elements (22,352 loci) in ASD blood using publicly-available Illumina Infinium 450K methylation datasets from heterogeneous ASD (n = 52), ASD with 16p11.2 del (n = 7), and ASD with Chromodomain Helicase DNA-binding 8 (CHD8) variants (n = 15). The differentially methylated positions of LINE-1 and Alu elements corresponding to genes were combined with transcriptome data from multiple ASD studies.Results We identified the epigenetic age acceleration significantly decelerated in ASD children over the age of 11 years. We further interrogated locus- and family-specific methylation profiles of LINE-1 and Alu elements (22,352 loci) in ASD blood using publicly-available Illumina Infinium 450K methylation datasets from heterogeneous ASD (n = 52), ASD with 16p11.2 del (n = 7), and ASD with Chromodomain Helicase DNA-binding 8 (CHD8) variants (n = 15). DNA methylation profiling revealed LINE-1 and Alu methylation signatures in each ASD risk loci by which global methylation were notably hypomethylated exclusively in ASD with CHD8 variants. When LINE-1 and Alu elements were clustered into subfamilies, we found methylation changes in a family-specific manner in L1P, L1H, HAL, AluJ, and AluS families in the heterogeneous ASD and ASD with CHD8 variants. Interesting, our results showed that LINE-1 and Alu methylation within target genes is inversely related to the expression level in each ASD variant. Finally, we demonstrate the potential for LINE-1 and Alu methylation signatures to predict ASD individuals from non-ASD. ConclusionsThe DNA methylation signatures of the LINE-1 and Alu elements in ASD, as well as their functional impact on ASD-related genes, have been identified. If confirmed in future larger studies, these finding may contribute to the identification of epigenomic biomarkers of ASD in those with high risk of ASD.

BackgroundLong interspersed nucleotide element-1 (LINE-1) and Alu elements are retrotransposons whose abilities cause abnormal gene expression and genomic instability. Several studies have focused on DNA methylation profiling of gene regions, but the locus-specific methylation of LINE-1 and Alu elements has not been identified in autism spectrum disorder (ASD).MethodsHere, DNA methylation age was predicted using Horvath’s method. We interrogated locus- and family-specific methylation profiles of LINE-1 and Alu elements (22,352 loci) in ASD blood using publicly-available Illumina Infinium 450K methylation datasets from heterogeneous ASD (n = 52), ASD with 16p11.2 del (n = 7), and ASD with Chromodomain Helicase DNA-binding 8 (CHD8) variants (n = 15). The differentially methylated positions of LINE-1 and Alu elements corresponding to genes were combined with transcriptome data from multiple ASD studies. ROC curve was conducted to examine the specificity of target loci.ResultsEpigenetic age acceleration was significantly decelerated in ASD children over the age of 11 years. DNA methylation profiling revealed LINE-1 and Alu methylation signatures in each ASD risk loci by which global methylation were notably hypomethylated exclusively in ASD with CHD8 variants. When LINE-1 and Alu elements were clustered into subfamilies, we found methylation changes in a family-specific manner in L1P, L1H, HAL, AluJ, and AluS families in the heterogeneous ASD and ASD with CHD8 variants. Our results showed that LINE-1 and Alu methylation within target genes is inversely related to the expression level in each ASD variant. Moreover, LINE-1 and Alu methylation signatures can be used to predict ASD individuals from non-ASD.LimitationsIntegration of methylome and transcriptome datasets was performed from different ASD cohorts. The small sample size of the validation cohort used post-mortem brain tissues and necessitates future validation in a larger cohort.ConclusionsThe DNA methylation signatures of the LINE-1 and Alu elements in ASD, as well as their functional impact on ASD-related genes, have been studied. These findings are considered for further research into DNA methylation profiles and the expression of the LINE-1 and Alu elements in post-mortem brain tissue, which has been linked to ASD pathogenesis.

Alu elements are transposable elements that can influence gene regulation through several mechanisms; nevertheless, it remains unclear whether dysregulation of Alu elements contributes to the neuropathology of autism spectrum disorder (ASD). In this study, we characterized transposable element expression profiles and their sequence characteristics in the prefrontal cortex tissues of ASD and unaffected individuals using RNA-sequencing data. Our results showed that most of the differentially expressed transposable elements belong to the Alu family, with 659 loci of Alu elements corresponding to 456 differentially expressed genes in the prefrontal cortex of ASD individuals. We predicted cis- and trans-regulation of Alu elements to host/distant genes by conducting correlation analyses. The expression level of Alu elements correlated significantly with 133 host genes (cis-regulation, adjusted p < 0.05) associated with ASD as well as the cell survival and cell death of neuronal cells. Transcription factor binding sites in the promoter regions of differentially expressed Alu elements are conserved and associated with autism candidate genes, including RORA. COBRA analyses of postmortem brain tissues showed significant hypomethylation in global methylation analyses of Alu elements in ASD subphenotypes as well as DNA methylation of Alu elements located near the RNF-135 gene (p < 0.05). In addition, we found that neuronal cell density, which was significantly increased (p = 0.042), correlated with the expression of genes associated with Alu elements in the prefrontal cortex of ASD. Finally, we determined a relationship between these findings and the ASD severity (i.e., ADI-R scores) of individuals with ASD. Our findings provide a better understanding of the impact of Alu elements on gene regulation and molecular neuropathology in the brain tissues of ASD individuals, which deserves further investigation.