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One of the major challenges of cocaine addiction is the high rate of relapse to drug use after periods of withdrawal. During the first few weeks of withdrawal, cue-induced cocaine craving intensifies, or "incubates," and persists over extended periods of time. Although several brain regions and molecular mechanisms were found to be involved in this process, the underlying epigenetic mechanisms are still unknown. Herein, we used a rat model of incubation of cocaine craving, in which rats were trained to self-administer cocaine (0.75 mg/kg, 6h/d, 10d), and cue-induced cocaine-seeking was examined in an extinction test after 1 or 30 d of withdrawal. We show that the withdrawal periods, as well as cue-induced cocaine seeking, are associated with broad, time-dependent enhancement of DNA methylation alterations in the nucleus accumbens (NAc). These gene methylation alterations were partly negatively correlated with gene expression changes. Furthermore, intra-NAc injections of a DNA methyltransferase inhibitor (RG108, 100μM) abolished cue-induced cocaine seeking on day 30, an effect that persisted 1 month, whereas the methyl donor S-adenosylmethionine (500μM) had an opposite effect on cocaine seeking. We then targeted two proteins whose genes were demethylated by RG108-estrogen receptor 1 (ESR1) and cyclin-dependent kinase 5 (CDK5). Treatment with an intra-NAc injection of the ESR1 agonist propyl pyrazole triol (10 nM) or the CDK5 inhibitor roscovitine (28μM) on day 30 of withdrawal significantly decreased cue-induced cocaine seeking. These results demonstrate a role for NAc DNA methylation, and downstream targets of DNA demethylation, in incubation of cocaine craving. [ABSTRACT FROM AUTHOR]

Early-life adversity is associated with a broad scope of life-long health and behavioral disorders. Particularly critical is the role of the mother. A possible mechanism is that these effects are mediated by “epigenetic” mechanisms. Studies in rodents suggest a causal relationship between early-life adversity and changes in DNA methylation in several “candidate genes” in the brain. This study examines whether randomized differential rearing (maternal vs surrogate–peer rearing) of rhesus macaques is associated with differential methylation in early adulthood. The data presented here show that differential rearing leads to differential DNA methylation in both prefrontal cortex and T cells. These differentially methylated promoters tend to cluster by both chromosomal region and gene function. The broad impact of maternal rearing on DNA methylation in both the brain and T cells supports the hypothesis that the response to early-life adversity is system-wide and genome-wide and persists to adulthood. Our data also point to the feasibility of studying the impact of the social environment in peripheral T-cell DNA methylation. [ABSTRACT FROM AUTHOR]

Maternal care alters epigenetic programming of glucocorticoid receptor (GR) gene expression in the hippocampus, and increased postnatal maternal licking/grooming (LG) behavior enhances nerve growth factor-inducible protein A (NGFI-A) transcription factor binding to the exon 17GR promoter within the hippocampus of the offspring. We tested the hypothesis that NGFI-A binding to the exon 17GR promoter sequence marks this sequence for histone acetylation and DNA demethylation and that such epigenetic alterations subsequently influence NGFI-A binding and GR transcription. We report that (1) NGFI-A binding to its consensus sequence is inhibited by DNA methylation, (2) NGFI-A induces the activity of exon 17GR promoter in a transient reporter assay, (3) DNA methylation inhibits exon 17GR promoter activity, and (4) whereas NGFI-A interaction with the methylated exon 17GR promoter is reduced, NGFI-A overexpression induces histone acetylation, DNA demethylation, and activation of the exon 17GR promoter in transient transfection assays. Site-directed mutagenesis assays demonstrate that NGFI-A binding to the exon 17GR promoter is required for such epigenetic reprogramming. In vivo, enhanced maternal LG is associated with increased NGFI-A binding to the exon 17GR promoter in the hippocampus of pups, and NGFI-A-bound exon 17GR promoter is unmethylated compared with unbound exon 17GRpromoter. Knockdown experiments of NGFI-A in hippocampal primary cell culture show that NGFI-A is required for serotonin-induced DNA demethylation and increased exon 17GR promoter expression. The data are consistent with the hypothesis that NGFI-A participates in epigenetic programming of GR expression. [ABSTRACT FROM AUTHOR]

Stress responses in the adult rat are programmed early in life by maternal care and associated with epigenomic marking of the hippocampal exon 17 glucocorticoid receptor (GR) promoter. To examine whether such epigenetic programming is reversible in adult life, we centrally infused the adult offspring with the essential amino acid L-methionine, a precursor to S-adenosyl-methionine that serves as the donor of methyl groups for DNA methylation. Here we report that methionine infusion reverses the effect of maternal behavior on DNA methylation, nerve growth factor-inducible protein-A binding to the exon 17 promoter, GR expression, and hypothalamic-pituitary- adrenal and behavioral responses to stress, suggesting a causal relationship among epigenomic state, GR expression, and stress responses in the adult offspring. These results demonstrate that, despite the inherent stability of the epigenomic marks established early in life through behavioral programming, they are potentially reversible in the adult brain. [ABSTRACT FROM AUTHOR]