All-trans retinoic acid-induced hypothalamus-pituitary-adrenal hyperactivity involves glucocorticoid receptor dysregulation

Abstract

Clinical reports have highlighted a role for retinoids in the etiology of mood disorders. Although we had shown that recruitment of the nuclear receptor retinoic acid receptor (RAR) to corticotropin-releasing hormone (CRH) promoter is implicated in activation of the hypothalamus-pituitary-adrenal (HPA) axis, further insight into how retinoids modulate HPA axis activity is lacking. Here we show that all-trans retinoic acid (RA)-induced HPA activation involves impairments in glucocorticoid receptor (GR) negative feedback. RA was applied to rats chronically through intracerebroventricular injection. A 19-day RA exposure induced potent HPA axis activation and typical depression-like behavior. Dexamethasone failed to suppress basal corticosterone (CORT) secretion, which is indicative of a disturbed GR negative feedback. In the hypothalamic paraventricular nucleus, increased CRH + and c-fos + cells were found while a negative R-2 +/ER + correlation was present between the number of RAR + and GR + cells. This was paralleled by increased RAR and decreased GR protein expression in the hypothalamus. Additional in vitro studies confirmed that RA abolished GR-mediated glucocorticoid-induced suppression of CRH expression, indicating a negative cross-talk between RAR and GR signaling pathways. Finally, the above changes could be rapidly normalized by treatment with GR antagonist mifepristone. We conclude that in addition to the 'classic' RAR-mediated transcriptional control of CRH expression, disturbances in GR negative feedback constitute a novel pathway that underlies RA-induced HPA axis hyperactivity. The rapid normalization by mifepristone may be of potential clinical interest in this respect. © 2013 Macmillan Publishers Limited.