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 1 7 GR promoter within the hippocampus of the offspring. We tested the hypothesis that NGFI-A binding to the exon 1 7 GR 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 1 7 GR promoter in a transient reporter assay, (3) DNA methylation inhibits exon 1 7 GR promoter activity, and (4) whereas NGFI-A interaction with the methylated exon 1 7 GR promoter is reduced, NGFI-A overexpression induces histone acetylation, DNA demethylation, and activation of the exon 1 7 GR promoter in transient transfection assays. Site-directed mutagenesis assays demonstrate that NGFI-A binding to the exon 1 7 GR promoter is required for such epigenetic reprogramming. In vivo, enhanced maternal LG is associated with increased NGFI-A binding to the exon 1 7 GR promoter in the hippocampus of pups, and NGFI-A-bound exon 1 7 GR promoter is unmethylated compared with unbound exon 1 7 GR promoter. Knockdown experiments of NGFI-A in hippocampal primary cell culture show that NGFI-A is required for serotonin-induced DNA demethylation and increased exon 1 7 GR promoter expression. The data are consistent with the hypothesis that NGFI-A participates in epigenetic programming of GR expression.

Parenting and the early environment influence the risk for various psychopathologies. Studies in the rat suggest that variations in maternal care stably influence DNA methylation, gene expression, and neural function in the offspring. Maternal care affects neural development, including the GABAergic system, the function of which is linked to the pathophysiology of diseases including schizophrenia and depression. Postmortem studies of human schizophrenic brains have revealed decreased forebrain expression of glutamic acid decarboxylase 1 (GAD1) accompanied by increased methylation of a GAD1 promoter. We examined whether maternal care affects GAD1 promoter methylation in the hippocampus of adult male offspring of high and low pup licking/grooming (high-LG and low-LG) mothers. Compared with the offspring of low-LG mothers, those reared by high-LG dams showed enhanced hippocampal GAD1 mRNA expression, decreased cytosine methylation, and increased histone 3-lysine 9 acetylation (H3K9ac) of the GAD1 promoter. DNA methyltransferase 1 expression was significantly higher in the offspring of low-compared with high-LG mothers. Pup LG increases hippocampal serotonin (5-HT) and nerve growth factor-inducible factor A (NGFI-A) expression. Chromatin immunoprecipitation assays revealed enhanced NGFI-A association with and H3K9ac of the GAD1 promoter in the hippocampus of high-LG pups after a nursing bout. Treatment of hippocampal neuronal cultures with either 5-HT or an NGFI-A expression plasmid significantly increased GAD1 mRNA levels. The effect of 5-HT was blocked by a short interfering RNA targeting NGFI-A. These results suggest that maternal care influences the development of the GABA system by altering GAD1 promoter methylation levels through the maternally induced activation of NGFI-A and its association with the GAD1 promoter.

Variations in parental care direct phenotypic development across many species. Variations in maternal pup licking/grooming (LG) in the rat regulate the development of individual differences in hypothalamic -pituitary-adrenal responses to stress. The adult offspring of mothers that show an increased frequency of pup LG have increased hippocampal glucocorticoid receptor (GR) expression and more modest pituitary -adrenal responses to stress. This parental effect is mediated by the epigenetic programming of a GR exon 1 promoter (exon 1 7 ) through the binding of the transcription factor nerve growth factor-inducible factor A (NGFI-A). In this paper, we report that: (i) the association of NGFI-A with the exon 1 7 GR promoter is dynamically regulated by mother -pup interactions; (ii) this effect is mimicked by artificial tactile stimulation comparable to that provided by pup LG; (iii) that serotonin (5-HT) induces an NGFI-A-dependent increase in GR transcription in hippocampal neurons and NGFI-A overexpression is sufficient for this effect; and (iv) that thyroid hormones and 5-HT are key mediators of the effects of pup LG and tactile stimulation on NGFI-A binding to the exon 1 7 GR promoter in hippocampus. These findings suggest that pup LG directly activates 5-HT systems to initiate intracellular signalling pathways in the hippocampus that regulate GR transcription.

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