Effect of dexamethasone on Na+/Ca2+ exchanger in dendritic cells

Ca(+)-dependent signaling regulates the function of dendritic cells (DCs), antigen-presenting cells linking innate and adaptive immunity. The activity of DCs is suppressed by glucocorticoids, potent immunosuppressive hormones. The present study explored whether the glucocorticoid dexamethasone influences the cytosolic Ca(2+) concentration ([Ca(2+)](i)) in DCs. To this end, DCs were isolated from mouse bone marrow. According to fura-2 fluorescence, exposure of DCs to lipopolysaccharide (LPS, 100 ng/ml) increased [Ca(2+)](i), an effect significantly blunted by overnight incubation with 10 nM dexamethasone before LPS treatment. Dexamethasone did not affect the Ca(2+) content of intracellular stores, sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA)2 and SERCA3 expression, ryanodine receptor (RyR)1 expression, or Ca(2+) entry through store-operated Ca(2+) channels. In contrast, dexamethasone increased the transcript level and the membrane protein abundance of the Na(+)/Ca(2+) exchanger NCX3. The activity of Na(+)/Ca(2+) exchangers was assessed by removal of extracellular Na(+) in the presence of external Ca(2+), a maneuver triggering the Ca(2+) influx mode. Indeed, Na(+) removal resulted in a rapid transient increase of [Ca(2+)](i) and induced an outwardly directed current as measured in whole cell patch-clamp experiments. Dexamethasone significantly augmented the increase of [Ca(2+)](i) and the outward current following removal of extracellular Na(+). The NCX blocker KB-R7943 reversed the inhibitory effect of dexamethasone on LPS-induced increase in [Ca(2+)](i). Dexamethasone blunted LPS-induced stimulation of CD86 expression and TNF-α production, an effect significantly less pronounced in the presence of NCX blocker KB-R7943. In conclusion, our results show that glucocorticoid treatment blunts LPS-induced increase in [Ca(2+)](i) in DCs by increasing expression and activity of Na(+)/Ca(2+) exchanger NCX3. The effect contributes to the inhibitory effect of the glucocorticoid on DC maturation.