Salt-sensitivity of blood pressure is an independent risk factor for cardiovascular disease and affects approximately half of the hypertensive population. While the precise mechanisms of salt-sensitivity remain unclear, recent findings on body sodium homeostasis and salt-induced immune cell activation provide new insights into the relationship between high salt intake, inflammation, and hypertension. The immune system, specifically antigen-presenting cells (APCs) and T cells, are directly implicated in salt-induced renal and vascular injury and hypertension. Emerging evidence suggests that oxidative stress and activation of the NLRP3 inflammasome drive high sodium-mediated activation of APCs and T cells and contribute to the development of renal and vascular inflammation and hypertension. In this review, we summarize the recent insights into our understanding of the mechanisms of salt-sensitive hypertension and discuss the role of inflammasome activation as a potential therapeutic target.

Nearly 30% of adults consume less than the estimated average daily requirement of magnesium (Mg2+), and commonly used medications, such as diuretics, promote Mg2+ deficiency. Higher serum Mg2+ levels, increased dietary Mg2+ in-take, and Mg2+ supplementation are each associated with lower blood pressure, suggesting that Mg2+-deficiency contributes to the pathogenesis of hypertension. Antigen-presenting cells, such as monocytes and dendritic cells, are well-known to be involved in the pathogenesis of hypertension. In these cells, processes implicated as necessary for increased blood pressure include activation of the NLRP3 inflammasome, IL-1β production, and oxidative modification of fatty acids such as arachidonic acid, forming isolevuglandins (IsoLGs). We hypothesized that increased blood pressure in response to dietary Mg2+-depletion leads to increased NLRP3, IL-1β, and IsoLG production in antigen presenting cells. We found that a Mg2+-depleted diet (0.01% Mg2+ diet) increased blood pressure in mice compared to mice fed a 0.08% Mg2+ diet. Mg2+-depleted mice did not exhibit an increase in total body fluid, as measured by quantitative magnetic resonance. Plasma IL-1β concentrations were increased (0.13 ± 0.02 pg/mL vs. 0.04 ± 0.02 pg/mL). Using flow cytometry, we observed increased NLRP3 and IL-1β expression in antigen-presenting cells from spleen, kidney, and aorta. We also observed increased IsoLG production in antigen-presenting cells from these organs. Primary culture of CD11c+ dendritic cells confirmed that low extracellular Mg2+ exerts a direct effect on these cells, stimulating IL-1β and IL-18 production. The present findings show that NLRP3 inflammasome activation and IsoLG-adduct formation are stimulated when dietary Mg2+ is depleted. Interventions and increased dietary Mg2+ consumption may prove beneficial in decreasing the prevalence of hypertension and cardiovascular disease.

Introduction: Salt sensitivity of blood pressure is a phenomenon in which blood pressure changes according to dietary sodium intake. Our previous studies found that high salt activates antigen presenting cells, resulting in the development of hypertension. The mechanisms by which salt-induced immune cell activation is regulated in salt sensitivity of blood pressure are unknown. In the current study, we investigated dietary salt-induced effects on the renin-angiotensin-aldosterone system (RAAS) gene expression in myeloid immune cells and their impact on salt sensitive hypertension in humans.Methods: We performed both bulk and single-cell sequencing analysis on immune cells with in vitro and in vivo high dietary salt treatment in humans using a rigorous salt-loading/depletion protocol to phenotype salt-sensitivity of blood pressure. We also measured plasma renin and aldosterone using radioimmunoassay.Results: We found that while in vitro high sodium exposure downregulated the expression of renin, renin binding protein and renin receptor, there were no significant changes in the genes of the renin-angiotensin system in response to dietary salt loading and depletion in vivo. Plasma renin in salt sensitive individuals tended to be lower with a blunted response to the salt loading/depletion challenge as previously reported.Discussion: These findings suggest that unlike systemic RAAS, acute changes in dietary salt intake do not regulate RAAS expression in myeloid immune cells.

Background: Salt-sensitivity of blood pressure puts both normotensive and hypertensive individuals at a higher risk for cardiovascular morbidity and mortality. Isolevuglandins (IsoLGs) have been shown to be increased in multiple oxidative-stress associated diseases, including salt-sensitive hypertension. We had previously reported that mice who received adoptive transfer of DCs exposed to high salt exhibited a prohypertensive response, which was abolished when these DCs were pretreated with IsoLG specific scavenger, 2-HOBA. Additionally, we found that scavenging of IsoLGs using 2-HOBA in a mouse model of salt-sensitive hypertension blocked NLRP3 inflammasome in dendritic cells (DCs). Whether IsoLGs directly lead to NLRP3 inflammasome activation remain unknown. IsoLGs have been shown to adduct to histones, specifically H4 histones. Histones are responsible for regulating chromatin structure. However, it is unknown how IsoLG-modified histones affect gene transcription. We tested the hypothesis that elevated sodium in APCs leads to IsoLG-adducted H4 histones increasing transcriptional access to NLRP3 inflammasome components contributing to salt-sensitive hypertension. Methods: In vitro studies were performed on isolated monocytes from 11 hypertensive individuals treated with either normal salt (150mM) or high salt (190mM) and submitted for RNA sequencing. In vivo studies were performed on 19 hypertensive subject enrolled in an acute inpatient protocol to assess response to salt loading (460 mmoL/24 hours) and salt depletion (10 mmoL/24 hours, and furosemide 40 mg x 3). IsoLG-containing DCs were identified using flow cytometry as CD45+MerTK-HLADR+CD1c+. Isolated PBMCs from a salt sensitive subject (ΔSBPSD-SL = -12.9) and a salt resistant subject (ΔSBPSD-SL = 0.35) were analyzed using assay for transposase-accessible chromatin with high-throughput sequencing (ATACseq). Results: Using RNA sequencing data of isolated monocytes and the EpiFactors database, I identified differentially expressed genes related to histones and histone modification. This analysis demonstrated an overall upregulation in histone modification after high salt visualized in a heatmap and PCA plot, specifically upregulation of gene HIST4H4 which encodes the Histone H4 (25.4 ± 4.6 vs 65.5 ± 6.5, [n=11, q=1.5 x 10-3, paired analyses and adjusted P values (q), false discovery rate (<0.05)]). Changes in IsoLG-containing DCs during the salt sensitivity protocol correlated with ΔSBP (R2=0.25, p=0.03). The ATACseq data showed gene expression and promoter sum, a measure of chromatin availability, of inflammasome component NLRP3 were more salt responsive in DCs of the salt-sensitive subject versus the salt-resistant subject after salt depletion. Conclusions: Variability in ΔIsoLG may be a future biomarker for SSBP. Our results suggest the high [Na+] increase in IsoLG-adducts may epigenetically regulate NLRP3 inflammasome components in SSBP. No Disclosures. Funding Sources: K01HL130497, R01HL147818, R03HL155041, R01HL144941 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.