Prolonged Access to Cocaine Results in Distinct Epigenetic Changes in the Prefrontal Cortex (LB622)

Abstract

DNA methylation is a key determinant of gene expression and is implicated in neuroplasticity relevant to addiction. Here, we examine DNA methylation and mRNA expression for two genes, Homer2 and NPAS4, within the dorsal medial prefrontal cortex (dmPFC) following saline, short‐access (1h), or prolonged‐access (6h), to cocaine during self‐administration. As reported previously, only 6h rats exhibited escalated cocaine intake across sessions. Initial MeDIP‐CHIP analyses of dmPFC tissue by ChIPMonk software revealed dramatic and extremely gene‐specific changes in DNA methylation/demethylation within promoter regions and flanking the transcription start site (TSS). The Homer2 and NPAS4 promoters showed active changes in DNA methylation following 6h and 1h cocaine self‐administration compared to saline. A follow‐up analysis, via sodium bisulphite conversion followed by mass spectrophotometry interrogating a 1000bp sequence of the Homer2 promoter, confirmed increased methylation of CpG7 in the 6h rats, which contains putative consensus sequences for GATA‐1 and p300. Additionally, MeDIP followed by qPCR revealed an increase in DNA methylation for both 1h and 6h rats within the 457‐645bp upstream of the NPAS4 transcription start site (TSS).qPCR revealed an increase in Homer2 mRNA levels in the 6h versus 1h and saline conditions, and a decrease in NPAS4 mRNA in 1h and 6h versus saline conditions. These results demonstrate that prolonged cocaine self‐administration alters DNA methylation of the Homer2 and NPAS4 gene promoters within the dmPFC in a distinct manner. Additionally, the altered DNA methylation leads to decreases in NPAS4 mRNA and increases in Homer2 mRNA expression within the dmPFC. Given the known roles of Homer2 as a scaffolding protein for the metabotropic glutamate 1 and 5 (mGluR1/5) receptors and NPAS4 as a transcription factor promoting inhibitory synapse formation, these data indicate that excessive cocaine intake induces changes in gene regulation for inhibitory and excitatory synapses. Thus, excessive cocaine intake induces a distinct change in DNA methylation which may contribute the long‐term alterations in brain function associated with addiction.Grant Funding Source: NIH R21DA027115