High Salt Activates Dendritic Cells to Promote Hypertension

Abstract

Both inflammation and dietary salt intake have been implicated in the pathogenesis of hypertension. We have previously shown that the formation of immunogenic isoketal‐protein adducts in dendritic cells (DCs) plays an important role in the development of experimental hypertension. Recently, it has been shown that salt can accumulate in the interstitial space and promote inflammation. In the current study, we tested the hypothesis that exposure to high salt drives DCs toward an activated state, leading to the production of immunogenic isoketals and the promotion of hypertension. To test this hypothesis, mouse splenic DCs were cultured in media with either normal salt (NS, 150 mM NaCl) or high salt (HS, 190 mM NaCl) for 24 hours. Exposure to HS caused a 2‐fold increase in superoxide production in DCs compared to NS. This was NADPH oxidase‐dependent since incubation with the gp91ds‐tat peptide prevented the increase. HS exposure also led to an increase in the activation markers CD80 and CD86, and doubled the number of DCs containing isoketal‐protein adducts. Moreover, DCs exposed to HS but not NS drove proliferation of both CD4+ (5198.2±2398.6 vs. 15.3±7.1 proliferated cells, p<0.01) and CD8+ (25381.6±9495.6 vs. 9.8±4.1 proliferated cells, p<0.01) T cells. None of these effects were mediated by increased osmolality as addition of mannitol (80 mM) to the media had no effect. Western blots of protein extracts from DCs indicated that all NADPH subunits (p47phox, p22phox, gp91phox and p67phox) were increased by exposure of cells to HS, and that these effects were prevented by inhibition of the serum‐and‐glucocorticoid‐inducible kinase‐1 (SGK1). In additional experiments, mice received adoptive transfer of splenic DCs that were cultured for 24 hours in either NS (n = 5); HS (n = 5); HS plus the SGK1 inhibitor, GSK 650394 (HS+GSK, n = 5) or HS plus the isoketal scavenger, 2‐hydroxybenzylamine (HS+2‐HOBA, n=5). Mice were then implanted with radiotelemeters to measure arterial pressure. Following recovery and two days of baseline, subcutaneous osmotic minipumps were implanted for administration of a generally sub‐pressor dose of angiotensin II (140 ng/kg/min). This caused no increase in blood pressure in mice that received NS DCs, whereas mean arterial pressure increased significantly (14 ± 4 mmHg, p<0.05) by one week of angiotensinogen II infusion in mice that received salt‐activated DCs. The pro‐hypertensive effect of salt on DCs was completely blocked by inhibition of SGK1 and scavenging of isoketals during their salt exposure. Taken together, our data indicate that DCs can be activated by exposure to a high salt environment which can exist in pro‐hypertensive states, and that this likely involves increased NADPH oxidase mediated superoxide production and formation of isoketal‐protein adducts. Moreover, high salt exposure can cause DCs to become pro‐hypertensive. These studies define a new pathway linking salt to immune activation and identify a previously undefined role of SGK1 in this process.Support or Funding InformationThis work is supported by National Institutes of Health grants R01HL039006, P01HL058000, P01HL095070, P01GM015431, R01HL108701, R01HL105294, VITA award HHSN268201400010C and the Strategically Focused Research Network Award from the American Heart Association.