Reduced Gene Dosage of the Psychiatric Risk Gene Is Associated with Impairments in Hypothalamic-Pituitary-Adrenal Axis Activity in Rats.

Common and rare variation in gene expression has been consistently associated with neuropsychiatric disorders such as schizophrenia, bipolar disorder, and major depression. However, the underlying biological pathways that cause this association have yet to be fully determined. In this study, we present evidence that rats with a reduced gene dosage of have increased basal corticosterone levels in the periphery and reduced the expression of encoding the glucocorticoid receptor in the hippocampus and hypothalamus. These results are consistent, with an effect of dosage on hypothalamus-pituitary-adrenal (HPA) axis function. Heterozygous rats had lower levels of the histone markers H3K4me3 and H3K27acat exon 1 of the gene. These histone modifications are typically linked to increased gene expression, but here were not associated with changes in the expression of exon 1 variants under non-stress conditions. Heterozygous rats additionally show increased anxiety behaviours. These results support an association of heterozygosity with the altered activity of the HPA axis and function in the resting state, and this may be a predisposing mechanism that contributes to the increased risk of psychiatric disorders with stress.