High Salt Promotes Human Monocytes Activation In Vitro and In Vivo

The mechanisms by which salt causes hypertension are poorly understood. We recently found that dendritic cells (DCs), potent antigen presenting cells, sense salt through amiloride-sensitive channels leading to activation of the NADPH oxidase and formation of immunogenic isolevuglandin (IsoLG)-protein adducts. DCs cultured in a HS environment and adaptively transferred to mice prime the hypertensive response to a sub-pressure dose of angiotensin II. To translate our animal finds to humans, we tested the hypothesis that increased NaCl activates human monocytes to a DC-like inflammatory phenotype. We exposed monocytes from 17 human volunteers to normal physiological NaCl (NS: 150 mM/L), elevated NaCl (HS: 190 mM/L), or an equiosmoloar concentration of mannitol. Exposure of human monocytes to high salt, but not mannitol, increased formation of IsoLG-adducts (mean fluorescent intensities - NS: 1688±384, Mann: 1762±429, HS: 2381± 635 Mean± SEM, p<0.002) as well as the expression of DC markers including CD83 (NS:0.75±0.2 vs HS: 1.1 ±0.3 %, p=0.03), CD1c (NS:0.42±0.15 vs HS:0.96±0.3%, p=0.01) and CD209 (NS: 3.1±0.8 vs HS:5.2±1.0%, p=0.008), while inhibition of NADPH oxidase with the peptide gp91dstat prevented the increase in CD1c and CD209 expression. Salt also induced production of inflammatory cytokines including IL-1β, IL-6 and TNF-α. Monocytes exposed to salt drive T cell proliferation measured by KI67 expression (CD8 NS: 678± 108 vs HS:1019 ±151, p=0.02 and CD4 NS:710±110 and HS:1048±157 MFI p=0.02) and production of IL-17A in both CD8 (intracellular staining: NS: 0.6±0.2 vs HS: 1±0.3 % p=0.01) and CD4 cells (NS: 0.2±0.5 vs HS: 0.4±0.08 % p=0.008). The propensity for monocytes to respond to NaCl was influenced by the patient's risk factors. The increase in IsoLG (HS-NS) correlated with pulse pressure (mmHg, r=0.51, <0.04), BMI (Kg/m2, r=0.66, p=0.005), total cholesterol (mg/dL, r=0.55, p<0.05) and glucose (mg/dL, r=0.72, p=0.003). In a second cohort of subjects, 70 prehypertensive subjects were recruited and 23Na magnetic resonance imaging (23Na MRI) was used to visualize their skin sodium stores. We found that subjects with higher skin sodium concentration had increased formation of IsoLG-adducts in their monocytes (NS: 23.7±5.9 HS: 38.8 ± 6.3 % p<0.001) and higher percentage of cells expressing the dendritic cell marker CD83 (NS: 0.04± 0.001 vs HS: 0.12± 0.03 % p=0.04). These data strongly support our in vitro findings showing that the interstitial hypertonicity drives monocytes activation. Our findings suggest that high extracellular NaCl promotes differentiation and activation of monocytes and that these pleotropic inflammatory cells exhibit a previously undefined salt sensitivity corresponding to patients' underlying risk factor profile. Support or Funding Information AHA Postdoctoral Award Number: 16POST29090001 This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.