Role of glucocorticoids and glucocorticoid receptor in priming of macrophages caused by glucocorticoid receptor blockade

Abstract

We previously reported that glucocorticoid receptor (GR) blockade (injected with GR antagonist RU486) primed the host responses to lipopolysaccharide. Since decrease of GR and elevated glucocorticoids (GCs) have been always reported as parallel responses, we hypothesize that both GCs and GR play important roles in GR blockade induced priming. We first confirm that the production of nitric oxide (NO), superoxide (O2-), and PKCalpha expression are all increased in peritoneal macrophages from GR blockade rats, indicating that macrophages are primed by GR blockade. Furthermore, using unilateral adrenalectomy rats, we find that the elevated GCs caused by a feedback mechanism following GR blockade may be involved in the process of priming. In vitro experiments in RAW264.7 cells show the inhibitory effect of GCs on NO production, which can be thoroughly blocked by RU486, indicating the increase of NO production in GR blockade rats is due to the elimination of GCs's anti-inflammatory function. In contrast, 10(-7) M corticosterone induces significant increases in O2- release, PKCalpha expression and phosphorylation, which cannot be reversed by RU486, demonstrating a previously unrecognized pro-inflammatory role of GCs in enhancing PM activation through a GR-independent pathway. The effect of GCs on PKCalpha expression even exists in GR deficient COS-7 cells as well as in GR knock-down RAW264.7 cells. In conclusion, both GR impairment and elevation of GCs are involved in the priming of macrophages caused by GR blockade. The findings of the divergent roles of GCs in modulation of inflammation may change therapeutic strategy for inflammatory diseases with GCs.