Comparison of Human Brain Persistent Organic Pollutant Levels with Epigenetic Alterations in DNA Methylation and MeCP2

Background: Epigenetics act at the interface of genetic and environmental factors in autism risk. Several autism-spectrum disorders have genetic mutations in gene or gene loci regulated by epigenetic mechanisms, including X-linked Rett syndrome (RTT, MECP2), and imprinted chromosomal region 15q11-13 disorders Prader-Willi (PWS) and Angelman syndromes (AS). Aberrant DNA methylation has previously been observed at the MECP2 promoter in autism male brain, as well as epigenetic alterations in expression of the 15q11-13 GABAA receptor genes. Persistent organic pollutants (POPs), including polychlorinated biphenyls (PCBs) and polybrominated diphenylethers (PBDEs) bioaccumulate in fat and lipid-rich tissues, and thus are of particular concern for the effects on neurodevelopment. High organic pollutant exposures in Greenlandic Inuits have previously been associated with reduced global DNA methylation. Objectives: Investigate epigenetic alterations in DNA methylation and MeCP2 levels in human cortex samples from control, autism, and other neurodevelopmental disorders to test the hypothesis that exposures to POPs may correlate with epigenetic changes. Methods: PBDEs were analysed by GC/MS using NCI (negative chemical ionization) and PCBs were analysed by GC/uECD (micro electron capture detector) on human post mortem cortex and cerebellum frozen samples. Levels of pollutants were normalized to lipid content in each brain sample. To investigate global DNA methylation, 5-Methyl-Cytosine immunofluorescence was detected by laser scanning cytometry (LSC) and normalized to control mouse IgG staining on each tissue samples arranged on a tissue microarray. Results: Preliminary data on 25 control, 16 autism, and 27 other genetic disorders (combined RTT, PWS, AS, and DS) brain samples show that BDE-47 is the most abundant PBDE congener in all groups included in this study, followed by BDE-99, -153 and -100. PCB congeners as a group were much lower than PBDEs in the same samples. Autism samples showed significantly lower levels of PCB-118, -138, and -153 compared to controls. PBDE levels were not significantly different in autism, but showed a trend towards lower levels of BDE-47, -99, and -183 compared to controls. An additional 32 brain samples are currently being analyzed to test a potential significance of PBDE levels in autism brain samples. Autism samples showed higher levels of global DNA methylation compared to controls both in the MeCP2-hi and total cell populations on the tissue microarray. A correlation analysis of each PBDE congener with DNA methylation levels will be performed. Conclusions: While POPs, particularly PBDE-47, are detectable in human brain samples, autism brain samples show lower levels of several PCBs and a trend for lower levels of PBDEs. Our preliminary data supports other work in blood suggesting an inverse correlation between POP exposure and global DNA methylation levels.