Early life stress-induced histone acetylations correlate with activation of the synaptic plasticity genes Arc and Egr1 in the mouse hippocampus

Early life stress (ELS) programs the developing organism and influences the development of brain and behavior. We tested the hypothesis that ELS-induced histone acetylations might alter the expression of synaptic plasticity genes that are critically involved in the establishment of limbic brain circuits. Maternal separation (MS) from postnatal day 1416 was applied as ELS and two immediate early genes underlying experience-induced synaptic plasticity, Arc and early growth response 1 (Egr1) were analyzed. We show here that repeated ELS induces a rapid increase of Arc and Egr1 in the mouse hippocampus. Furthermore, immunoblotting revealed that these changes are paralleled by histone modifications, reflected by increased acetylation levels of H3 and H4. Most importantly, using native Chromatin immunoprecipitation quantitative PCR (nChIP-qPCR), we show for the first time a correlation between elevated histone acetylation and increased Arc and Egr1 expression in response to ELS. These rapid epigenetic changes are paralleled by increases of dendritic complexity and spine number of hippocampal CA3 pyramidal neurons in ELS animals at weaning age. Our results are in line with our working hypothesis that ELS induces activation of synaptic plasticity genes, mediated by epigenetic mechanisms. These events are assumed to represent early steps in the adaption of neuronal networks to a stressful environment.