Common schizophrenia risk variants are implicated in the function of glutamatergic neurons

The epigenome of human brain cells encompasses key information in understanding brain function in both healthy and diseased states. To further explore this, we used ATAC-seq to profile chromatin structure in four distinct populations of cells (glutamatergic neurons, GABAergic neurons, oligodendrocytes, and microglia/astrocytes), from three different regions of the brain. Chromatin accessibility was found to vary vastly by cell type and, more moderately, by brain region, with glutamatergic neurons showing the greatest regional variability. Transcription factor footprinting pointed to cell-specific transcriptional regulators and inferred cell-specific regulation of protein coding genes, long intergenic noncoding RNAs, and microRNAs. In vivo transgenic mouse experiments validated the cell type specificity of a number of human-derived regulatory sequences. Open chromatin regions in glutamatergic neurons were enriched for neuropsychiatric risk variants, particularly those associated with schizophrenia. Combining differential chromatin accessibility analysis using ATAC-seq data from bulk tissue increased our statistical power to confirm glutamatergic neurons as the cell type most affected in schizophrenia. Jointly, these findings illustrate the utility of studying the cell type specific epigenome in complex tissues such as the human brain and implicate an association among chromatin accessibility in glutamatergic neurons and genetic risk for schizophrenia. Open chromatin profiles in neuronal and non-neuronal nuclei from 3 brain regions, 4 cell types of 4 control samples