Barbier E1, *Johnstone AL3,4, Khomtchouk BB3,4, Tapocik JD2, Pitcairn C2, Rehman F2, Augier E1, Borich A2, Schank JR6, Rienas CA3,4, Van Booven DJ5, Sun H2, Nätt D1 , Wahlestedt C3,4, Heilig M1
1Department of Clinical and Experimental Medicine, Division of Cell Biology, Faculty of Health Sciences, Linköping University, SE-581 85 Linköping, Sweden
2Laboratory of Clinical and Translational Studies, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, Maryland;
3The Center for Therapeutic Innovation,
4Department of Psychiatry & Behavioral Sciences, and the
5John P. Hussman Institute for Human Genomics, University of Miami Miller School of Medicine, Miami FL
6Department of Physiology and Pharmacology, College of Veterinary Medicine, The University of Georgia, Athens, GA
Alcohol dependence leads to escalation of alcohol seeking and intake. We have shown that this is in part driven by a coordinated and persistent dysregulations of gene expression networks in the medial prefrontal cortex (mPFC). Recent work in our laboratory has identified contributions to these processes from microRNA (Tapocik et al, J Neurosci 2014) and DNA-methyl transferase activity (Barbier et al, J Neurosci 2015), but little is known about a potential role of other epigenetic enzymes in reprogramming the mPFC transcriptome.
Recently (Barbier et al, Mol Psychiat in press), we used RNA-sequencing to screen the transcriptome of the mPFC for persistent differential expression of epigenetic enzymes, and identified PRDM2 as a candidate. In rats with a history of dependence, both the RNA-seq screen and a focused confirmatory qPCR analysis showed decreased expression of PRDM2. Immunohistochemical analysis indicated that this occurred in neurons. Alcohol-induced PRDM2 repression was reversed by the DNA methyltransferase inhibitor RG108, suggesting that it is driven by DNA methylation. Conversely, PRDM2 knockdown in non-dependent rats induced a set of gene expression changes that overlapped with those found following alcohol dependence. These expression changes were associated with behavioral consequences otherwise seen following a history of dependence, including escalated alcohol intake, increased resistance to quinine adulteration, and enhanced stress-induced reinstatement. Several genes that exhibited a significantly decreased enrichment for H3K9me1 (a functional consequence of PRDM2 repression) were identified using ChIP-seq study, including synaptotagmin 1 (Syt1).
In summary, we report the discovery of PRDM2 as a mediator of neuroadaptations and behaviors that are critical in alcoholism. Specifically, our findings indicate that DNA-methylation mediated repression of PRDM2 is involved in multiple aspects of alcohol dependence, including stress-induced relapse, compulsivity-like behavior and escalation in alcohol intake.