Epigenetic signatures of autism: Trimethylated H3K4 landscapes in prefrontal neurons

Context: Neuronal dysfunction in cerebral cortex and other brain regions could contribute to the cognitive and behavioral defects in autism. Objective: To characterize epigenetic signatures of autism in prefrontal cortex neurons. Design:Weperformed fluorescence-activated sorting and separation of neuronal and nonneuronal nuclei from postmortem prefrontal cortex, digested the chromatin with micrococcal nuclease, and deeply sequenced the DNA from the mononucleosomes with trimethylated H3K4 (H3K4me3), a histone mark associated with transcriptional regulation. Approximately 15 billion base pairs of H3K4me3-enriched sequences were collected from 32 brains. Setting: Academic medical center. Participants: A total of 16 subjects diagnosed as having autism and 16 control subjects ranging in age from 0.5 to 70 years. Main Outcome Measures: Identification of genomic loci showing autism-associated H3K4me3 changes in prefrontal cortex neurons. Results: Subjects with autism showed no evidence for generalized disruption of the developmentally regulated remodeling of the H3K4me3 landscape that defines normal prefrontal cortex neurons in early infancy. However, excess spreading of H3K4me3 from the transcription start sites into downstream gene bodies and upstream promoters was observed specifically in neuronal chromatin from 4 of 16 autism cases but not in controls. Variable subsets of autism cases exhibit altered H3K4me3 peaks at numerous genes regulating neuronal connectivity, social behaviors, and cognition, often in conjunction with altered expression of the corresponding transcripts. Autism-associated H3K4me3 peaks were significantly enriched in genes and loci implicated in neurodevelopmental diseases. Conclusions: Prefrontal cortex neurons from subjects with autism show changes in chromatin structures at hundreds of loci genome-wide, revealing considerable overlap between genetic and epigenetic risk maps of developmental brain disorders.