High Salt Activates Human Monocytes and Promotes their Conversion into Dendritic Cells via Formation of Immunogenic Isoketal‐adducts

Abstract

High blood pressure is a major modifiable risk factor for cardiovascular disease (CVD) which is the leading cause of death worldwide. Excessive salt intake and inflammation are implicated in the genesis of hypertension. It has recently become evident that sodium accumulates in the interstitial space and can promote inflammation through poorly defined mechanisms. We recently published a new pathway in which increased oxidative stress in dendritic cells (DCs) leads to formation of isoketal‐modified proteins which act as neo‐antigens to activate T cells. We hypothesized that increasing sodium chloride (NaCl) in excess of the physiological interstitial space concentrations activates antigen presenting cells via formation of immunogenic isoketals. We exposed monocytes from human volunteers to normal physiological NaCl (150 mM/L), elevated NaCl concentrations (190 mM/L), or an equiosmoloar concentration of mannitol. We found that exposure of human monocytes to high salt, but not mannitol, caused a 2‐fold increase in formation of isoketal‐modified proteins. This was associated with an increase in activation marker CD86 (466 ± 192 normal salt vs 596 ± 324 high salt) and production of inflammatory cytokines IL‐6, IL‐β and TNF‐α. Interestingly, these cells expressed surface markers indicative of transformation to DCs, as evidenced by their acquisition of surface marker CD83. In additional immunofluorescence studies, we found that monocytes exposed to high salt for 7 days acquire a DC like morphology. Moreover, using flow cytometry, we confirmed that high salt exposure causes these cells to lose the monocyte marker CD14, and gain the DC marker CD209. When co‐cultured with T cells from the same patients, these cells drive T cell proliferation. Scavenging of isoketals during high salt exposure prevented conversion of monocytes into DCs and their ability to drive T cell proliferation. Thus, we have defined a novel pathway whereby high NaCl concentrations lead to transformation of monocytes to DCs due to increased formation of immunogenic isoketals. These observations provide insight into how elevated sodium environments lead to an inflammatory state.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.