Epigenetic regulation of spermidine/spermine N1-acetyltransferase (SAT1) in suicide

We have recently shown that the expression of spermidine/spermine N1-acetyltransferase (SAT1) is downregulated across the brains of suicide completers, and that its expression is influenced by genetic variations in the promoter. Several promoter polymorphisms in SAT1, including rs6526342, have been associated with suicide and other psychiatric disorders, and display haplotype-specific effects on expression. However, these effects cannot explain total variability in SAT1 expression, and other regulatory mechanisms, such as epigenetic factors, may also be at play. In this study, we assessed the involvement of epigenetic factors in controlling SAT1 expression in the prefrontal cortex of suicide completers by mapping CpG methylation across a 1880-bp region of the SAT1 promoter, and measuring levels of tri-methylated histone-3-lysine 27 (H3K27me3) at the promoter in suicide completers and controls. Our results demonstrated that CpG methylation was significantly negatively correlated with SAT1 expression. Although overall or site-specific CpG methylation was not associated with suicide or SAT1 expression, we observed high levels of methylation at the polymorphic CpG site created by rs6526342, indicating a relationship between promoter haplotypes and methylation. There was no association between H3K27me3 and suicide, nor was this modification associated with SAT1 expression. Overall, our results indicate that epigenetic factors in the promoter region of SAT1 influence gene expression levels, and may provide a mechanism for both our previous findings of haplotype-specific effects of promoter variations on SAT1 expression, as well as the widespread downregulation of SAT1 expression observed in the brains of suicide completers.