Epigenetics of Fetal Brain Development in the Valproic Acid Model of Autism

Abstract

Use of the drug, valproic acid (VPA) by pregnant women increases the risk of autism in their children. This led to the development of the VPA mouse model of autism in which a pregnant dam is given a single dose of the drug at E12.5 which results in her offspring expressing autistic phenotypes. Our lab has found that using the in utero VPA model of autism results in a transient increase in Bdnf mRNA and protein in the mouse fetal brain. The goal of my research is to elucidate the epigenetic underpinnings of VPA and the related increased expression of the neurotrophin gene, Bdnf. VPA is a histone deacetylase inhibitor. Changes in histone acetylation engage in molecular crosstalk with other epigenetic marks and can result in alterations in histone and DNA methylation. Several histone modifications were analyzed using chromatin immunoprecipitation at three exons of interest, Bdnf exons 1, 4, and 6. A significant increase was found in each excitatory mark examined including acetylation of various histones as well as H3K4me3. Sex differences were found at some sites in histone acetylation and at most sites for H3K4me3. The greater increase in these activating marks was found in females. Two inhibitory marks were also analyzed, H3K27me3 and DNA CpG methylation. No effect of VPA was found on H3K27me3 and a small, but statistically significant effect was found on DNA methylation across four CpGs upstream of Bdnf exon 4. Bdnf transcript levels were measured in both sexes and found that there is more stimulation of exons 1 and 4 in females. Furthermore, we found that most stimulation of Bdnf transcript expression occurred in the caudal regions of the fetal brain and not the telencephalon. Together, these experiments help to elucidate the epigenetic contributions to VPA's ability to increase Bdnf expression in the brains of fetuses exposed to the drug in utero.