Regulation of Na+/H+ exchanger in dendritic cells by Akt2

Dendritic cells (DCs) are antigen-presenting cells decisive in primary immune responses and establishment of immunological memory. They are activated by bacterial lipopolysaccharides (LPS), which lead to activation of Na+/H+ exchanger activity, cell swelling, reactive oxygen species (ROS) formation, and migration. The effects require functional phosphoinositide 3 kinase and are paralleled by Akt phosphorylation. The present study explored the putative involvement of the Akt isoform Akt2. To this end, experiments were performed in DCs isolated from bone marrow of mice lacking functional Akt2/PKB (akt2 (-/-)) and respective wild-type animals (akt2 (+/+)). Based on BCECF fluorescence, cytosolic pH (pH(i)) was significantly lower in akt2 (-/-) than in akt2 (+/+) DCs. Transient exposure to NH4Cl was followed by profound cytosolic acidification in both genotypes. Subsequent re-alkalinization was largely dependent on Na+ thus reflecting Na+/H+ exchanger activity and was significantly lower in akt2 (-/-) than in akt2 (+/+) DCs. According to forward scatter in FACS analysis, cell volume was significantly lower in akt2 (-/-) than in akt2 (+/+) DCs. Exposure of DCs to LPS led within 4 h to significant increases of Na+/H+ exchanger activity, cell volume, ROS production, and migration in akt2 (+/+) mice, and its effects were significantly blunted in akt2 (-/-) DCs. The present observations disclose a role of Akt2 in the regulation of pH(i), cell volume, ROS production, and migration in dendritic cells.