Effect of Bacterial Lipopolysaccharide on Na⁺/H⁺ Exchanger Activity in Dendritic Cells

The function of dendritic cells (DCs), antigen-presenting cells linking innate and adaptive immunity, is stimulated by bacterial lipopolysaccharides (LPS), which trigger the formation of reactive oxygen species (ROS). In macrophages, ROS formation is paralleled by activation of the Na(+)/H(+) exchanger, a carrier involved in the regulation of cytosolic pH and cell volume. The present study explored whether LPS influence Na(+)/H(+) exchanger activity in DCs. The DCs were isolated from murine bone marrow, cell volume was estimated from forward scatter in FACS analysis, ROS production from 2',7'-dichlorodihydrofluorescein diacetate (DCFDA) fluorescence, apoptosis from annexin V binding, cytosolic pH (pH(i)) from 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF) fluorescence and Na(+)/H(+) exchanger activity from the Na(+) dependent realkalinization following an ammonium pulse. Exposure of DCs to LPS (1 μg/ml) led to a transient increase of Na(+)/H(+) exchanger activity. Moreover, LPS increased forward scatter and ROS formation and decreased apoptosis. The NHE1 inhibitor cariporide (10 μM) virtually abrogated Na(+)/H(+) exchanger activity, inhibited LPS-induced cell swelling, blunted LPS-induced ROS formation and reversed the antiapoptotic effect of LPS. Na(+)/H(+) exchanger activity was stimulated by oxidative stress and LPS induced stimulation of NHE activity was abolished in presence of ROS chelators (Tempol, Tiron and Vitamin C). In conclusion, LPS treatment transiently upregulates the Na(+)/H(+) exchanger in DCs, an effect required for the effects of LPS on DC survival, cell volume and ROS formation.