In a rodent model, research has emerged linking early environmental influence, i.e. variations in maternal care, to behavioral and neuroendocrine alterations in adult life (Meaney 2001; Weaver et al 2004). The offspring of rat mothers showing high maternal care were less fearful and showed reduced hypothalamus-pituitary-adrenal (HPA) axis responses to stress. The HPA axis is under tight self-regulating control through negative feedback mechanisms governed by the glucocorticoid receptor (GR). The reduced HPA axis responsiveness in offspring of high caring mothers was associated with increased hippocampal GR mRNA expression and enhanced glucocorticoid feedback sensitivity. Cross-fostering studies revealed that most of these effects are non-genomically transmitted from one generation to the other (Francis et al 1999). Subsequently, the mechanism was elucidated, showing that variations in maternal care lead to stable alterations of DNA methylation patterns. Low maternal care results in increased methylation of the nerve growth factor-inducible protein A (Ngfi-A) binding site located in the Nr3c1 gene exon 17 promoter, leading to decreased GR expression. Remarkably, expression of exon 17 containing mRNA seems to be unique to hippocampus, so that methylation of exon 17 specifically reduces Nr3c1 expression in hippocampal sites (Weaver et al 2004).
We investigated whether a similar biological mechanism can be observed in humans by analyzing post mortem tissue of 32 human hippocampi. Therefore we aimed to characterize the promoter region of the recently identified, rat orthologue human exon 1F (Turner and Muller 2005) of the human NR3C1. The proximal promoter was analyzed for putative NGFI-A transcription factor binding sites. Furthermore, analysis of methylation pattern was undertaken using bisulfite modification in order to answer the question whether differential methylation as shown in rats can also be observed in humans.
Own publications on the subject:
Moser D., Molitor A., Kumsta R., Riederer P., Tatschner T., Meyer J. (2007): The glucocorticoid receptor gene exon 1-F promoter is not methylated at the NGFI-A binding site in human hippocampus. World J. Biol. Psychiatry: 8:4, 262 - 268
Anne Molitor (2006): Untersuchung einer NGFI-A Bindungsstelle im Promotor des humanen Glucocorticoidrezeptorgens hinsichtlich potentieller Methylierung in post mortem Hippocampusgewebe. Diploma Thesis