Epigenetic regulation of the oxytocin system as an indicator of adaptation to over-controlling parenting and psychosocial functioning in adulthood.

The oxytocin system plays a role in social stress adaptation, and this role is likely to be particularly important in adolescence. One method of regulating the oxytocin system is through DNA methylation in the promoter of the oxytocin receptor gene (OXTRm), which reduces the gene's expression. This multi-method, longitudinal study, using a diverse community sample of 184 adolescents followed from age 13-28, examined the links between OXTRm and exposure to over-controlling parenting in adolescence and conflict with romantic partners and internalizing symptoms in adulthood. Female, but not male, adolescents who were exposed to psychologically controlling parenting at age 13 had lower levels of OXTRm at site -924 at age 28. Reduced OXTRm at site -924 was associated with greater romantic partner-reported relationship conflict at age 27, and reduced OXTRm at site -934 was marginally associated with greater participant-reported conflict for males. Reduced OXTRm at site -924 was also associated with fewer internalizing symptoms at ages 24-25. These results in adulthood are consistent with an upregulated oxytocin system reducing the salience of negative socioemotional stimuli. Overall, findings are consistent with oxytocin playing a role in the stress response system, and more specifically, by helping us to adapt to social environments like parenting and romantic relationships, reducing the salience of negativity, and reducing risk for common emotional problems.

Genetic, epigenetic, and environmental factors controlling oxytocin receptor gene expression.

BACKGROUND: The neuropeptide oxytocin regulates mammalian social behavior. Disruptions in oxytocin signaling are a feature of many psychopathologies. One commonly studied biomarker for oxytocin involvement in psychiatric diseases is DNA methylation at the oxytocin receptor gene (OXTR). Such studies focus on DNA methylation in two regions of OXTR, exon 3 and a region termed MT2 which overlaps exon 1 and intron 1. However, the relative contribution of exon 3 and MT2 in regulating OXTR gene expression in the brain is currently unknown. RESULTS: Here, we use the prairie vole as a translational animal model to investigate genetic, epigenetic, and environmental factors affecting Oxtr gene expression in a region of the brain that has been shown to drive Oxtr related behavior in the vole, the nucleus accumbens. We show that the genetic structure of Oxtr in prairie voles resembles human OXTR. We then studied the effects of early life experience on DNA methylation in two regions of a CpG island surrounding the Oxtr promoter: MT2 and exon 3. We show that early nurture in the form of parental care results in DNA hypomethylation of Oxtr in both MT2 and exon 3, but only DNA methylation in MT2 is associated with Oxtr gene expression. Network analyses indicate that CpG sites in the 3' portion of MT2 are most highly associated with Oxtr gene expression. We also identify two novel SNPs in exon 3 of Oxtr in prairie voles and a novel alternative transcript originating from the third intron of the gene. Expression of the novel alternative transcript is associated with genotype at SNP KLW2. CONCLUSIONS: These results identify putative regulatory features of Oxtr in prairie voles which inform future studies examining OXTR in human social behaviors and disorders. These studies indicate that in prairie voles, DNA methylation in MT2, particularly in the 3' portion, is more predictive of Oxtr gene expression than DNA methylation in exon 3. Similarly, in human temporal cortex, we find that DNA methylation in the 3' portion of MT2 is associated with OXTR expression. Together, these results suggest that among the CpG sites studied, DNA methylation of MT2 may be the most reliable indicator of OXTR gene expression. We also identify novel features of prairie vole Oxtr, including SNPs and an alternative transcript, which further develop the prairie vole as a translational model for studies of OXTR.

OXTR DNA methylation moderates the developmental calibration of neural reward sensitivity.

The Adaptive Calibration Model of Stress Responsivity (ACM) suggests that developmental experiences predictably tune biological systems to meet the demands of the environment. Particularly important is the calibration of reward systems. Using a longitudinal sample (N = 184) followed since adolescence, this study models the dimensions of early life stress and their effects on epigenetic modification of the oxytocin receptor gene (OXTR) and individual differences in neural response to reward anticipation. We first created a latent variable model of developmental context using measures collected when participants were 13 years old. As adults, two subsets of participants completed a reward anticipation fMRI paradigm (N = 82) and agreed to have their blood assayed for (OXTR) DNA methylation (N = 112) at two CpG sites. Three latent constructs of developmental context emerged: Neighborhood Harshness, Family Harshness, and Abuse and Disorder. Greater OXTR DNA methylation at CpG sites -924 and -934 blunted the association between greater Neighborhood Harshness and increased neural activation in caudate in anticipation of rewards. Interaction effects were also found outside of reward-related areas for all three latent constructs. Results indicate an epigenetically derived differential susceptibility model whereby high methylation coincides with decreased association between developmental environment and neural reward anticipation.

Early nurture epigenetically tunes the oxytocin receptor.

Mammalian sociality is regulated in part by the neuropeptide oxytocin. In prairie voles, subtle variation in early life experience changes oxytocin receptor-mediated social behaviors. We report that low levels of early care in voles leads to de novo DNA methylation at specific regulatory sites in the oxytocin receptor gene (Oxtr), impacting gene expression and protein distribution in the nucleus accumbens. DNA methylation state of the blood predicts expression in the brain indicating the utility of the blood as a biomarker for the transcription state of the brain. These experience-sensitive CpG sites are conserved in humans, are related to gene expression in the brain, and have been associated with psychiatric disorders and individual differences in neural response to social stimuli. These results identify a mechanism by which early care regulates later displays of typical prairie vole social behavior and suggest the potential for nurture driven epigenetic tuning of OXTR in humans.