Immune Mechanisms of Salt-Sensitive hypertension

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Project Summary: Salt-sensitivity of blood pressure (SSBP) is an independent risk factor for cardiovascular mortality not only in hypertensive, but also in normotensive adults. The diagnosis for SSBP is not feasible in the clinic due to lack of a simple diagnostic test, making it difficult to investigate therapeutic strategies. Most research efforts to understand the mechanisms of SSBP have focused on renal regulation of sodium (Na+). However, salt retention or plasma volume expansion are not enhanced in salt sensitive (SS) versus salt resistant (SR) individuals. In addition, over 70% of extracellular fluid is interstitial and therefore not directly controlled by renal salt and water excretion. Thus, further research is needed to understand the extrarenal mechanisms contributing to SSBP. We recently found that Na+ enters monocyte-derived dendritic cells through the amiloride sensitive epithelial Na+ channel (ENaC) and activates the NADPH oxidase leading to formation of highly reactive products of lipid oxidation known as isolevuglandins (IsoLGs). IsoLGs adduct to self-proteins and act as neoantigens, which activate T cells to produce cytokines that promote Na+ retention and blood pressure (BP) elevation. Interestingly, analogous to SSBP, we found considerable variability in the response of human monocytes to in vitro exposure to elevated Na+ which correlated with known cardiovascular risk factors. It is not known if this variability in the responsiveness of monocytes to elevated Na+ happens in vivo and if it contributes to the SSBP. Recent studies found that Na+ accumulates in the interstitium electrostatically bound to glycosaminoglycans but can be mobilized. This is relevant to circulating monocytes as they enter and re-emerge from the interstitium with increased ability to present antigens. Our data indicate that monocytes from humans with high skin Na+ are activated and have increased IsoLGs. This R01 proposal presents an opportunity to study how immune activation and interstitial Na+ interact to impact SSBP in well phenotyped SS and SR individuals. We hypothesize that circulating monocytes transmigrate into regions of elevated Na+ including the skin, muscle and kidney, and are activated via IsoLG-adduct formation leading to SSBP. In Aim 1, we will employ an inpatient Weinberger protocol to classify participants as SS or SR and measure tissue Na+ using 23NaMRI to determine if tissue Na+ and monocyte activation contribute to SSBP. In Aim 2, we will adoptively transfer monocytes with T cells from SS and SR people into immunodeficient NSG-(KbDb)null (IA)null mice and determine if monocytes from humans with SSBP induce T cell activation, endothelial dysfunction, end-organ damage and SSBP in the humanized mice. These translational studies will advance the field and reveal more feasible and cost-effective diagnostic and therapeutic strategies for SSBP. Our exciting preliminary data indicating that changes in monocyte IsoLGs mirror changes in BP in response to salt provide promise for not only a simple diagnostic tool, but also mechanistic insight into the pathogenesis of SSBP. Alongside efforts to develop therapies for SSBP by focusing on the kidney, we propose that interstitial Na+ and monocyte activation via IsoLGs are important targets.