Annexin A1 mediates the effects of dexamethasone on macula densa cyclooxygenase‐2 expression

Abstract

In the present study we aimed to elucidate the role of the anti‐inflammatory protein annexin A1 (ANXA1) in the regulation of macula densa (MD) cyclooxygenase‐2 (COX‐2) expression by dexamethasone (Dex). To this end, cultured mouse macula densa cells (MMDD1) were treated for 8h with 0.1μM Dex. The presence of ANXA1, COX‐2, the ANXA1 receptor FPRL1, and the ANXA1 transporter ABCA1 was verified by PCR. Dex‐dependent changes in MMDD1 COX‐2 and ANXA1 expression were studied by TaqMan real time PCR. ANXA1 secretion was quantified by Western blotting of cell‐culture supernatant. To study the effects of ANXA1 receptor signalling on macula densa COX‐2 expression cells were treated either with the ANXA1 receptor agonist fMLP (1μM) or the ANXA1 receptor antagonist cyclosporin H (CyH; 0.1μM) for 8h. MMDD1 cells express COX‐2, ANXA1, ABCA1, and FPRL1. Treatment with Dex reduced COX‐2 mRNA abundance to 63±5% of controls (p<.05) whereas ANXA1 mRNA expression and protein secretion were increased to 156±10% and 360±19% of control, respectively (p<.05). COX‐2 mRNA expression was reduced by fMLP (66±6% of control; p<.05) and increased by CyH (183±33% of control; p<.05). In summary we have shown that Dex treatment increases MD ANXA1 expression and secretion. Stimulation of the ANXA1 receptor FPRL1 reduces COX‐2 mRNA expression. Our results thus suggest that the inhibitory effects of Dex on MD COX‐2 expression are mediated by ANXA1.