Regulation of Na+/H+ Exchanger in Dendritic Cells by Akt1
Background/Aims: Dendritic cells (DCs), antigen-presenting cells critically important for primary immune response and establishment of immunological memory, are activated by bacterial lipopolysaccharides (LPS) resulting in stimulation of Na<sup>+</sup>/H<sup>+</sup> exchanger, ROS formation and migration. The effects are dependent on phosphoinositide 3 (PI3) kinase and paralleled by Akt phosphorylation. The present study explored the contribution of the Akt isoform Akt1. Methods: Cytosolic pH (pH<sub>i</sub>) (2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein [BCECF] fluorescence), Na<sup>+</sup>/H<sup>+</sup> exchanger activity (Na<sup>+</sup> dependent realkalinization after an ammonium pulse), cell volume (forward scatter in FACS analysis), and ROS production (2′,7′-dichlorodihydrofluorescein diacetate [DCFDA] fluorescence) were determined in DCs isolated from bone marrow of mice lacking functional Akt1/PKBα (akt1<sup>-/-</sup>) and their wild type littermates (akt1<sup>+/+</sup>). Results: Forward scatter was lower in akt1<sup>-/-</sup> than in akt1<sup>+/+</sup> DCs, whereas pH<sub>i</sub>, Na<sup>+</sup>/H<sup>+</sup> exchanger activity and ROS formation were less in untreated akt1<sup>-/-</sup> and akt1<sup>+/+</sup> DCs. Exposure of DCs to LPS was followed by increase of forward scatter and ROS formation to a similar extent in akt1<sup>-/-</sup> and in akt1<sup>+/+</sup> DCs. A 4 hours treatment with either LPS (1µg/ml) or tert-butylhydroperoxide (tBOOH, 5 µM) significantly stimulated Na<sup>+</sup>/H<sup>+</sup> exchanger activity in both genotypes, effects, however, significantly blunted in akt1<sup>-/-</sup> DCs. Conclusion: The present observations demonstrate that Akt1 is required for the full stimulation of Na<sup>+</sup>/H<sup>+</sup> exchanger activity by LPS or oxidative stress in dendritic cells.