DC ENaC-Dependent Inflammasome Activation Contributes to Salt-Sensitive Hypertension

BACKGROUND

Salt sensitivity of blood pressure is an independent predictor of cardiovascular morbidity and mortality. The exact mechanism by which salt intake increases blood pressure and cardiovascular risk is unknown. We previously found that sodium entry into antigen-presenting cells (APCs) via the amiloride-sensitive epithelial sodium channel EnaC (epithelial sodium channel) leads to the formation of IsoLGs (isolevuglandins) and release of proinflammatory cytokines to activate T cells and modulate salt-sensitive hypertension. In the current study, we hypothesized that ENaC-dependent entry of sodium into APCs activates the NLRP3 (NOD [nucleotide-binding and oligomerization domain]-like receptor family pyrin domain containing 3) inflammasome via IsoLG formation leading to salt-sensitive hypertension.

METHODS

We performed RNA sequencing on human monocytes treated with elevated sodium in vitro and Cellular Indexing of Transcriptomes and Epitopes by Sequencing analysis of peripheral blood mononuclear cells from participants rigorously phenotyped for salt sensitivity of blood pressure using an established inpatient protocol. To determine mechanisms, we analyzed inflammasome activation in mouse models of deoxycorticosterone acetate salt-induced hypertension as well as salt-sensitive mice with ENaC inhibition or expression, IsoLG scavenging, and adoptive transfer of wild-type dendritic cells into NLRP3 deficient mice.

RESULTS

We found that high levels of salt exposure upregulates the NLRP3 inflammasome, pyroptotic and apoptotic caspases, and IL (interleukin)-1β transcription in human monocytes. Cellular Indexing of Transcriptomes and Epitopes by Sequencing revealed that components of the NLRP3 inflammasome and activation marker IL-1β dynamically vary with changes in salt loading/depletion. Mechanistically, we found that sodium-induced activation of the NLRP3 inflammasome is ENaC and IsoLG dependent. NLRP3 deficient mice develop a blunted hypertensive response to elevated sodium, and this is restored by the adoptive transfer of NLRP3 replete APCs.

CONCLUSIONS

These findings reveal a mechanistic link between ENaC, inflammation, and salt-sensitive hypertension involving NLRP3 inflammasome activation in APCs. APC activation via the NLRP3 inflammasome can serve as a potential diagnostic biomarker for salt sensitivity of blood pressure.

Bile acids and salt-sensitive hypertension: a role of the gut-liver axis

Salt-sensitivity of blood pressure (SSBP) affects 50% of the hypertensive and 25% of the normotensive populations. Importantly, SSBP is associated with increased risk for mortality in both populations independent of blood pressure. Despite its deleterious effects, the pathogenesis of SSBP is not fully understood. Emerging evidence suggests a novel role of bile acids in salt-sensitive hypertension and that they may play a crucial role in regulating inflammation and fluid volume homeostasis. Mechanistic evidence implicates alterations in the gut microbiome, the epithelial sodium channel (ENaC), the farnesoid X receptor, and the G protein-coupled bile acid receptor TGR5 in bile acid-mediated effects on cardiovascular function. The mechanistic interplay between excess dietary sodium-induced alterations in the gut microbiome and immune cell activation, bile acid signaling, and whether such interplay may contribute to the etiology of SSBP is still yet to be defined. The main goal of this review is to discuss the potential role of bile acids in the pathogenesis of cardiovascular disease with a focus on salt-sensitive hypertension.

Leukotriene B4 stimulation of an early elevation of phosphatidic acid mass in human neutrophils

The signal transduction pathway of leukotriene B4 involves phospholipase D activation in cytochalasin B-primed neutrophils, but leukotriene B4 stimulation of increased phosphatidic acid mass in neutrophils has not been demonstrated. Employing the NIH Image program, we have examined the effect of leukotriene B4 on phosphatidic acid mass in human neutrophils incubated with or without cytochalasin B. Our results show that 0.15 microM leukotriene B4 without cytochalasin B was capable of increasing phosphatidic acid mass in neutrophils by 2-fold after 5 s, 2.5-fold after 1 min, and 2-fold after 5 min incubation. Leukotriene B3, leukotriene B4, and leukotriene B5 were equipotent stimuli for phosphatidic acid mass elevation. Leukotriene B4 induced phosphatidylethanol formation at the expense of phosphatidic acid in cells preincubated with 0.25-1% ethanol, indicating phospholipase D activation. Cytochalasin B enhanced leukotriene B4 stimulation of phosphatidic acid mass elevation and phosphatidylethanol formation. There were no measurable changes in 1,2-diglyceride mass after 5 s, but a 1.7-fold increase occurred after 1 min and declined thereafter. Leukotriene B4 stimulation of [3H]glycerol incorporation into phosphatidic acid, diglyceride and phosphatidylinositol was detectable after a 1-min incubation, suggesting increased de novo synthesis of these lipids. These results suggest that leukotriene B4 stimulation of phospholipase D activity contributes to part of the early increased phosphatidic acid mass and that combined actions of stimulated phospholipases C and D, and de novo phosphatidic acid synthesis contribute to the total increased phosphatidic acid mass.

comparison of the efficacy of HS-6 versus HI-6 when combined with atropine, pyridostigmine and clonazepam for soman poisoning in the monkey

Monkeys were exposed to varying doses of soman and given therapy. Therapy consisted of pyridostigmine, clonazepam, atropine and HS-6 or HI-6. Cerebral electrical activity, heart rate, respiration, systemic blood pressure and cholinesterase activity were recorded thoughtout the experiment. The animals in the HS-6 series were divided into 4 groups depending upon the dose of soman; one group received 30 microgram/kg of soman, the second group received 40 microgran/kg. All animals in the HI06 series survived while only one of three monkeys in the fourth group survived. Administration of therapy immediately suppressed all seizure activity and convulsions and the animals appeared awake throughout the experiment. All animals exhibited bradycardia and hypotension following the adminstration of therapy. The cholinesterase activity was depressed after administration of HS-6 therapy. Three of the four monkey that received therapy consisting of HI-6 at a dose of 15 mg/kg survived, while one of two that received HI-6 at a dose of 30 mg/kg survived. The animals that received HI-6 at a dose of 15 mg/kg did not exhibit as severe a decrease in blood pressure as the animals in either the HS-6 series or the monkeys that received HI-6 at 30 mg/kg. In addition, these monkeys were awake and appeared alert throughout the experiment and were up within 4-6 hr post-exposure to soman. The animals that received 30 mg/kg exhibited severe hypotension and did poorly.