Glucocorticoids alter adrenomedullin receptor expression and secretion in endothelial-like cells and astrocytes

Adrenomedullin (AM) is a novel vasodilatory peptide, which acts primarily through the calcitonin receptor-like receptor (CLR) in combination with either receptor-activity-modifying-protein (RAMP) 2 or 3 (forming receptors, AM1 and AM2 respectively). AM is also highly expressed in the brain and it has shown neuropeptide characteristics. Furthermore, AM plays an important role during inflammation. Interestingly, AM secretion and AM receptor expression had also proven to be glucocorticoid (GC)-dependent in a variety of cell types, suggesting an intriguing relationship between the two compounds that needed to be further characterized. Protein studies have never been carried out in endothelial cells and neither have astrocytes been thoroughly investigated. Hence we studied the effect of GC treatments on AM secretion and AM-sensitivity in ECV304 an endothelial-like cell line and C6 rat astrocytes, focusing on receptor protein expression. We demonstrated that GCs could directly up-regulate RAMP2 expression intracellularly in endothelial cells. On the contrary, GCs were essential to maintain RAMP basal levels in astrocytes, where they could alter AM secretion within 24h. Although RAMP2 has shown to be similarly up-regulated also by AM exposure, no change in AM receptor expression was noted in C6 cells. In conclusion, our study indicates that GCs are able to regulate AM-sensitivity and AM secretion differently in endothelial-like cells and astrocytes. In particular, GCs altered RAMP2 in ECV304 cells, while affecting AM secretion in astrocytes, an interaction which could have interesting therapeutic implications for the blood-brain barrier regulation during both physiological and inflammatory conditions.