Environmental epigenomics, imprinting and disease susceptibility.

National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA.
Epigenetics: official journal of the DNA Methylation Society (Impact Factor: 5.11). 01/2006; 1(1):1-6. DOI: 10.4161/epi.1.1.2642
Source: PubMed
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    ABSTRACT: The molecular basis for the majority of cases of autism spectrum disorders (ASD) remains unknown. We tested the hypothesis that ASD have an epigenetic cause by performing DNA methylation profiling of 5 CpG islands (CGI-1 to CGI-5) in the SHANK3 gene in post mortem brain tissues from 54 ASD patients and 43 controls. We found significantly increased overall DNA methylation (epimutation) in three intragenic CGIs (CGI-2, CGI-3, and CGI-4). The increased methylation was clustered in the CGI-2 and CGI-4 in ∼15% of ASD brain tissues. SHANK3 has an extensive array of mRNA splice variants resulting from combinations of 5 intragenic promoters and alternative splicing of coding exons. Altered expression and alternative splicing of SHANK3 isoforms were observed in brain tissues with increased methylation of SHANK3 CGIs in ASD brain tissues. A DNA methylation inhibitor modified the methylation of CGIs and altered the isoform-specific expression of SHANK3 in cultured cells. This study is the first to find altered methylation patterns in SHANK3 in ASD brain samples. Our finding provides evidence to support an alternative approach to investigating the molecular basis of ASD. The ability to alter the epigenetic modification and expression of SHANK3 by environmental factors suggests that SHANK3 may be a valuable biomarker for dissecting the role of gene and environment interaction in the etiology of ASD.
    Human Molecular Genetics 11/2013; DOI:10.1093/hmg/ddt547 · 6.68 Impact Factor
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    ABSTRACT: Aberrant MeCP2 expression in brain is associated with neurodevelopmental disorders including autism. In the brain of stressed mouse and autistic human patients, reduced MeCP2 expression is correlated with Mecp2/MECP2 promoter hypermethylation. Altered expression of MeCP2 isoforms (MeCP2E1 and MeCP2E2) is associated with neurological disorders, highlighting the importance of proper regulation of both isoforms. While known regulatory elements (REs) within the MECP2/Mecp2 promoter and intron 1 are involved in MECP2/Mecp2 regulation, Mecp2 isoform-specific regulatory mechanisms are unknown. We hypothesized that DNA methylation at these REs may impact the expression of Mecp2 isoforms. We used a previously characterized in vitro differentiating neural stem cell (NSC) system to investigate the interplay between Mecp2 isoform-specific expression and DNA methylation at the Mecp2 REs. We studied altered expression of Mecp2 isoforms, affected by global DNA demethylation and remethylation, induced by exposure and withdrawal of decitabine (5-Aza-2[prime]-deoxycytidine). Further, we performed correlation analysis between DNA methylation at the Mecp2 REs and the expression of Mecp2 isoforms after decitabine exposure and withdrawal. At different stages of NSC differentiation, Mecp2 isoforms showed reciprocal expression patterns associated with minor, but significant changes in DNA methylation at the Mecp2 REs. Decitabine treatment induced Mecp2e1/MeCP2E1 (but not Mecp2e2) expression at day (D) 2, associated with DNA demethylation at the Mecp2 REs. In contrast, decitabine withdrawal downregulated both Mecp2 isoforms to different extents at D8, without affecting DNA methylation at the Mecp2 REs. NSC cell fate commitment was minimally affected by decitabine under tested conditions. Expression of both isoforms negatively correlated with methylation at specific regions of the Mecp2 promoter, both at D2 and D8. The correlation between intron 1 methylation and Mecp2e1 (but not Mecp2e2) varied depending on the stage of NSC differentiation (D2: negative; D8: positive). Our results show the correlation between the expression of Mecp2 isoforms and DNA methylation in differentiating NSC, providing insights on the potential role of DNA methylation at the Mecp2 REs in Mecp2 isoform-specific expression. The ability of decitabine to induce Mecp2e1/MeCP2E1, but not Mecp2e2 suggests differential sensitivity of Mecp2 isoforms to decitabine and is important for future drug therapies for autism.
    Molecular Autism 11/2013; 4(1):46. DOI:10.1186/2040-2392-4-46 · 5.49 Impact Factor
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    ABSTRACT: Autism remains an idiopathic disorder in 90% of cases. Recent prevalence, heritability, and genetic studies are suggestive that epigenetic and, therefore, environmental factors are important in autism pathogenesis. Among the environmental factors, only some uncommon viral infections and certain drugs have been conclusively linked to autism causation. Thalidomide, valproate, terbutaline and, most recently, antidepressants are the main drugs reported to elevate autism risk. This article discusses a phenomenal relationship between the drugs reported to elevate autism risk and the antiproliferative effects of the same drugs and/or analogs of the drugs in cancer cells. Cancer treatment has entered a new era-epigenetic therapy. In cancer cell lines, thalidomide is antiangiogenic and antiproliferative via suppression of tumor necrosis factor-alpha (TNF-α) and downstream effects on the nuclear factor (NFκB) cascade. Valproate shares similar mechanisms with thalidomide, but is best known in cancer therapy for its epigenetic effects as a histone deacetylase inhibitor. Terbutaline, a beta-adrenergic agonist, acts via adenylyl cyclase and cAMP-PKA signal transduction. Current cancer therapy aims to exploit this epigenetic pathway by developing site-selective cAMP analogs. Last, it has long been noted in preclinical studies that some antidepressants are antiproliferative in cancer cells but the mechanisms remain unclear. Based on a systematic review of these drugs, it is hypothesized that all central nervous system-acting drugs, which show antiproliferative effects in cancer cell lines, share the potential to elevate autism risk when administered prenatally. It is further posited that, in autism, the drugs act as "triggers" that disturb the pro-proliferative fetal milieu using the same, mainly epigenetic, mechanisms that they demonstrate in rapidly proliferating cancer cells. In addition to their direct antiproliferative effects, evidence is suggestive that the drugs may lock in the pro-inflammatory bias of the prenatal immune system by preventing normal perinatal dendritic cell maturation. This unifying hypothesis for how structurally different drugs elevate autism risk could help focus research on other drugs, or other xenobiotics, that may elevate autism risk. For example, there is evidence that an old class of drugs, the phenothiazines, is antiproliferative in cancer cell lines via inhibition of calmodulin and/or histaminic pathways. Promethazine, one of the first heterocyclic phenothiazines synthesized, is commonly prescribed during pregnancy; however, its role in elevating the risk of autism has not been investigated. Based on the anti-proliferation hypothesis, more studies of promethazine and other similar drugs are suggested to evaluate their potential to elevate autism risk following prenatal exposures.
    Medical Hypotheses 11/2013; 82(1). DOI:10.1016/j.mehy.2013.10.029 · 1.15 Impact Factor

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