Global DNA Methylation and Histone Posttranslational Modifications in Human and Nonhuman Primate Brain in Association with Prenatal Alcohol Exposure

Background Based upon experimental animal studies, the neurodevelopmental abnormalities associated with prenatal alcohol exposure (PNAE)/fetal alcohol spectrum disorder (FASD) have been attributed, at least in part, to epigenetic modifications. However, there are no direct analyses of human brain tissue. Methods Immunohistochemical detection of global epigenetic markers was performed on temporal lobe samples of autopsied fetuses and infants with documented PNAE. They were compared to age-, sex-, and postmortem delay-matched control cases (18 pairs; 20 to 70.5 weeks postconception). Temporal lobe tissue from a macaque monkey model of PNAE was also studied (5.7 to 6 months of age). We used antibodies targeting 4 DNA cytosine, 4 histone methylation, and 6 histone acetylation modifications and assigned scores based upon the semiquantitatively graded intensity and proportion of positively labeled nuclei in the ventricular and subventricular zones, ependyma, temporal cortex, temporal white matter, dentate gyrus (DG), and CA1 pyramidal layer. Results Temporal changes were identified for almost all marks according to the state of maturation in the human brain. In the DG (and 3 other brain regions), a statistically significant increase in H3K9ac was associated with PNAE. Statistically significant decreases were seen among 5mC, H3K4me3, H3K9ac, H3K27ac, H4K12ac, and H4K16ac in select regions. In the macaques, H3K36me3 decreased in the DG, and the ependyma showed decreases in 5fC and H3K36me3. Conclusions In human brain, global intranuclear epigenetic modifications are brain region and maturation state-specific. These exploratory results support the general hypothesis that PNAE is associated with a global decrease in DNA methylation, a global decrease in histone methylation, and a global increase in histone acetylation. Although the human and monkey subjects are not directly comparable in terms of brain maturation, considering the rapid temporal changes in global epigenetic modifications during brain development, interspecies comparisons may be extremely difficult.