Eicosanoid-Regulated Myeloid ENaC and Isolevuglandin Formation in Human Salt-Sensitive Hypertension.

BACKGROUND: The mechanisms by which salt increases blood pressure in people with salt sensitivity remain unclear. Our previous studies found that high sodium enters antigen-presenting cells (APCs) via the epithelial sodium channel and leads to the production of isolevuglandins and hypertension. In the current mechanistic clinical study, we hypothesized that epithelial sodium channel-dependent isolevuglandin-adduct formation in APCs is regulated by epoxyeicosatrienoic acids (EETs) and leads to salt-sensitive hypertension in humans. METHODS: Salt sensitivity was assessed in 19 hypertensive subjects using an inpatient salt loading and depletion protocol. Isolevuglandin-adduct accumulation in APCs was analyzed using flow cytometry. Gene expression in APCs was analyzed using cellular indexing of transcriptomes and epitopes by sequencing analysis of blood mononuclear cells. Plasma and urine EETs were measured using liquid chromatography-mass spectrometry. RESULTS: Baseline isolevuglandin+ APCs correlated with higher salt-sensitivity index. Isolevuglandin+ APCs significantly decreased from salt loading to depletion with an increasing salt-sensitivity index. We observed that human APCs express the epithelial sodium channel δ subunit, SGK1 (salt-sensing kinase serum/glucocorticoid kinase 1), and cytochrome P450 2S1. We found a direct correlation between baseline urinary 14,15 EET and salt-sensitivity index, whereas changes in urinary 14,15 EET negatively correlated with isolevuglandin+ monocytes from salt loading to depletion. Coincubation with 14,15 EET inhibited high-salt-induced increase in isolevuglandin+ APC. CONCLUSIONS: Isolevuglandin formation in APCs responds to acute changes in salt intake in salt-sensitive but not salt-resistant people with hypertension, and this may be regulated by renal 14,15 EET. Baseline levels of isolevuglandin+ APCs or urinary 14,15 EET may provide diagnostic tools for salt sensitivity without a protocol of salt loading.

Salt Sensitivity of Blood Pressure in Black People: The Need to Sort Out Ancestry Versus Epigenetic Versus Social Determinants of Its Causation.

Race is a social construct, but self-identified Black people are known to have higher prevalence and worse outcomes of hypertension than White people. This may be partly due to the disproportionate incidence of salt sensitivity of blood pressure in Black people, a cardiovascular risk factor that is independent of blood pressure and has no proven therapy. We review the multiple physiological systems involved in regulation of blood pressure, discuss what, if anything is known about the differences between Black and White people in these systems and how they affect salt sensitivity of blood pressure. The contributions of genetics, epigenetics, environment, and social determinants of health are briefly touched on, with the hope of stimulating further work in the field.

Regulation of human salt-sensitivite hypertension by myeloid cell renin-angiotensin-aldosterone system.

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.

Immune Profiling Reveals Decreases in Circulating Regulatory and Exhausted T Cells in Human Hypertension.

Evidence from nonhuman animal models demonstrates an important role for immune cells in hypertension, but immune cell changes in human hypertension are less clear. Using mass cytometry, we demonstrate novel and selective reductions in CCR10+ regulatory T cells (Tregs) and PD-1+CD57-CD8+ memory T cells. RNA sequencing reveals that CCR10+ Tregs exhibit gene expression changes consistent with enhanced immunosuppressive function. In addition, CITE-Seq demonstrates that PD-1+CD57-CD8+ memory T cells exhibit features of T-cell exhaustion. Taken together, these results provide novel evidence for decreases in anti-inflammatory and/or hypofunctional T-cell populations that may contribute to enhanced inflammation in human hypertension.

Sex differences in hypertension among people living with HIV after initiation of antiretroviral therapy.

Background: Hypertension is common in people living with HIV (PLWH) on antiretroviral therapy (ART). In the general population and in experimental animal models, the incidence of hypertension is greater in males than in females, especially during the premenopausal period. However, it is not known whether there are sex differences in hypertension associated with HIV and ART, and the factors contributing to incident hypertension among PLWH have not been well characterized. In this study, we aimed to determine the time course, sex differences and factors associated with incident hypertension in PLWH initiating ART. Methods and results: We conducted a retrospective study in which we used programmatic data from the ART registry to identify sex differences in the determinants of incident hypertension among PLWH initiating the ART regimen from Livingstone University Teaching Hospital in Zambia and followed for 8 years. Males developed hypertension earlier, 2 years after initiating ART, compared to 6 years in females. In multivariable analysis, increasing age, baseline systolic blood pressure and baseline mean arterial pressure (MAP) were associated with increased risk for developing incident hypertension. Also, participants who switched to the integrase strand transfer inhibitor, dolutegravir (DTG) or the protease inhibitor, lopinavir boosted with ritonavir were 2 and 3 times more likely to develop hypertension when compared to those on non-nucleoside reverse transcriptase inhibitors (NNRTIs). However, these relationships were abrogated by sex, as self-reported male sex was the major contributor in predicting incident hypertension. While none of the factors remained significantly associated with incident hypertension upon multivariate analysis among females, body mass index (BMI), and use of protease inhibitors remained strongly associated with hypertension among males. Conclusion: Our results indicate that the use of protease inhibitors and BMI are important predictors of incident hypertension among males. Thus, blood pressure and BMI should be closely monitored, particularly in males living with HIV on protease inhibitors. In addition, identifying specific factors that protect females from developing hypertension early is important but remains to be determined.

Immediate pressor response to oral salt and its assessment in the clinic: a time series clinical trial.

BACKGROUND: High blood pressure (BP) is associated with high-salt consumption especially in sub-Saharan Africa. Although the pressor effect of salt is viewed as a chronic effect, some studies suggest that a salty meal may increase BP immediately in some individuals, and that this effect may cause endothelial dysfunction. Therefore, the aim of our research was to study the immediate pressor response to oral salt (IPROS) and its determinants, with the expectation that a simple methodology may be devised to diagnose it in the clinic or in low-resource environments. METHODS: We conducted a time series trial at Livingstone Central Hospital. We present data in 127 normotensive participants who ingested 2 g of sodium chloride; their BP was monitored for 120 minutes in intervals of 10 minutes. Sociodemographic and clinical data were collected. Descriptive and inferential statistics were used for analyses of data. RESULTS: Median age was 30 years (interquartile range, 22-46 years) and 52% were female patients. An increase of ≥10 mmHg in mean arterial pressure (MAP), considered a clinically significant IPROS, was present in 62% of participants. Systolic BP 30 minutes after the salt load was a significant predictor of IPROS, avoiding the need to calculate MAP in the clinic setting. CONCLUSIONS: We confirm the presence of an IPROS in a high proportion (62%) of otherwise normotensive participants. The average time course for this response was 30 minutes and its duration was sustained for the 120-minutes period of study in most of the participants. Prediction of IPROS by ∆SBP (change in systolic blood pressure) at 30 minutes allows for easy assessment of possible responder status in the clinic. Our data indicate that the IPROS to oral salt-loads in the range currently consumed by the Western world and African populations in single meals may increase the 24-hour BP load, which is a risk factor for hypertension and target organ damage. The relevance of our findings indicates the need to include dietary sodium assessment in the diagnosis, prevention, and management of high BP.

Renal denervation in the antihypertensive arsenal - knowns and known unknowns.

Even though it has been more than a decade since renal denervation (RDN) was first used to treat hypertension and an intense effort on researching this therapy has been made, it is still not clear how RDN fits into the antihypertensive arsenal. There is no question that RDN lowers blood pressure (BP), it does so to an extent at best corresponding to one antihypertensive drug. The procedure has an excellent safety record. However, it remains clinically impossible to predict whose BP responds to RDN and whose does not. Long-term efficacy data on BP reduction are still unconvincing despite the recent results in the SPYRAL HTN-ON MED trial; experimental studies indicate that reinnervation is occurring after RDN. Although BP is an acceptable surrogate endpoint, there is complete lack of outcome data with RDN. Clear indications for RDN are lacking although patients with resistant hypertension, those with documented increase in activity of the sympathetic system and perhaps those who desire to take fewest medication may be considered.

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)-1ß transcription in human monocytes. Cellular Indexing of Transcriptomes and Epitopes by Sequencing revealed that components of the NLRP3 inflammasome and activation marker IL-1ß 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.

Recent advances in modulation of cardiovascular diseases by the gut microbiota.

The gut microbiota has recently gained attention due to its association with cardiovascular health, cancers, gastrointestinal disorders, and non-communicable diseases. One critical question is how the composition of the microbiota contributes to cardiovascular diseases (CVDs). Insightful reviews on the gut microbiota, its metabolites and the mechanisms that underlie its contribution to CVD are limited. Hence, the aim of this review was to describe linkages between the composition of the microbiota and CVD, CVD risk factors such as hypertension, diet, ageing, and sex differences. We have also highlighted potential therapies for improving the composition of the gut microbiota, which may result in better cardiovascular health.

Sox6, A Potential Target for MicroRNAs in Cardiometabolic Disease.

PURPOSE OF REVIEW: The study aims to review recent advances in knowledge on the interplay between miRNAs and the sex-determining Region Y (SRY)-related high-mobility-group box 6 (Sox6) in physiology and pathophysiology, highlighting an important role in autoimmune and cardiometabolic conditions. RECENT FINDINGS: The transcription factor Sox6 is an important member of the SoxD family and plays an indispensable role in adult tissue homeostasis, regeneration, and physiology. Abnormal expression of the Sox6 gene has been implicated in several disease conditions including diabetes, cardiomyopathy, autoimmune diseases, and hypertension. Expression of Sox6 is regulated by miRNAs, which are RNAs of about 22 nucleotides, and have also been implicated in several pathophysiological conditions where Sox6 plays a role. Regulation of Sox6 by miRNAs is important in diverse physiological tissues and organs. Dysregulation of the interplay between miRNAs and Sox6 is an important determinant of various disease conditions and may be actionable for therapeutic purposes.

Salt-Sensitivity of Blood Pressure and Insulin Resistance.

Salt sensitivity of blood pressure (SSBP) is an independent risk factor for cardiovascular morbidity and mortality that is seen in both hypertensive and normotensive populations. Insulin resistance (IR) strongly correlates with SSBP and affects nearly 50% of salt sensitive people. While the precise mechanism by which IR and SSBP relate remains elusive, several common pathways are involved in the genesis of both processes, including vascular dysfunction and immune activation. Vascular dysfunction associated with insulin resistance is characterized by loss of nitric oxide (NO)-mediated vasodilation and heightened endothelin-1 induced vasoconstriction, as well as capillary rarefaction. It manifests with increased blood pressure (BP) in salt sensitive murine models. Another common denominator in the pathogenesis of insulin resistance, hypertension, and salt sensitivity (SS) is immune activation involving pro-inflammatory cytokines like tumor necrosis factor (TNF)-α, IL-1ß, and IL-6. In the last decade, a new understanding of interstitial sodium storage in tissues such as skin and muscle has revolutionized traditional concepts of body sodium handling and pathogenesis of SS. We have shown that interstitial Na+ can trigger a T cell mediated inflammatory response through formation of isolevuglandin protein adducts in antigen presenting cells (APCs), and that this response is implicated in salt sensitive hypertension. The peroxisome proliferator-activated receptor γ (PPARγ) is a transcription factor that modulates both insulin sensitivity and BP. PPARγ agonists increase insulin sensitivity and ameliorate salt sensitivity, whereas deficiency of PPARγ results in severe insulin resistance and hypertension. These findings suggest that PPARγ plays a role in the common pathogenesis of insulin sensitivity and salt sensitivity, perhaps via effects on the immune system and vascular function. The goal of this review is to discuss those mechanisms that may play a role in both SSBP and in insulin resistance.

Salt Sensitivity of Blood Pressure in Blacks and Women: A Role of Inflammation, Oxidative Stress, and Epithelial Na+ Channel.

Significance: Salt sensitivity of blood pressure (SSBP) is an independent risk factor for mortality and morbidity due to cardiovascular disease, and disproportionately affects blacks and women. Several mechanisms have been proposed, including exaggerated activation of sodium transporters in the kidney leading to salt retention and water. Recent Advances: Recent studies have found that in addition to the renal epithelium, myeloid immune cells can sense sodium via the epithelial Na+ channel (ENaC), which leads to activation of the nicotinamide adenine dinucleotide phosphate oxidase enzyme complex, increased fatty acid oxidation, and production of isolevuglandins (IsoLGs). IsoLGs are immunogenic and contribute to salt-induced hypertension. In addition, aldosterone-mediated activation of ENaC has been attributed to the increased SSBP in women. The goal of this review is to highlight mechanisms contributing to SSBP in blacks and women, including, but not limited to increased activation of ENaC, fatty acid oxidation, and inflammation. Critical Issues: A critical barrier to progress in management of SSBP is that its diagnosis is not feasible in the clinic and is limited to expensive and laborious research protocols, which makes it difficult to investigate. Yet without understanding the underlying mechanisms, this important risk factor remains without treatment. Future Directions: Further studies are needed to understand the mechanisms that contribute to differential blood pressure responses to dietary salt and find feasible diagnostic tools. This is extremely important and may go a long way in mitigating the racial and sex disparities in cardiovascular outcomes. Antioxid. Redox Signal. 35, 1477-1493.

Immune Mechanisms of Dietary Salt-Induced Hypertension and Kidney Disease: Harry Goldblatt Award for Early Career Investigators 2020.

Salt sensitivity of blood pressure is an independent risk factor for cardiovascular mortality not only in hypertensive but also in normotensive adults. The diagnosis of salt sensitivity of blood pressure 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 salt sensitivity of blood pressure have focused on renal regulation of sodium. However, salt retention or plasma volume expansion is not different between salt-sensitive and salt-resistant individuals. In addition, over 70% of extracellular fluid is interstitial and, therefore, not directly controlled by renal salt and water excretion. We discuss in this review how the seminal work by Harry Goldblatt paved the way for our attempts at understanding the mechanisms that underlie immune activation by salt in hypertension. We describe our findings that sodium, entering antigen-presenting cells via an epithelial sodium channel, triggers a PKC (protein kinase C)- and SGK1 (serum/glucocorticoid kinase 1)-stimulated activation of nicotinamide adenine dinucleotide phosphate oxidase, which, in turn, enhances lipid oxidation with generation of highly reactive isolevuglandins. Isolevuglandins adduct to proteins, with the potential to generate degraded peptide neoantigens. Activated antigen-presenting cells increase production of the TH17 polarizing cytokines, IL (interleukin)-6, IL-1ß, and IL-23, which leads to differentiation and proliferation of IL-17A producing T cells. Our laboratory and others have shown that this cytokine contributes to hypertension. We also discuss where this sodium activation of antigen-presenting cells may occur in vivo and describe the multiple experiments, with pharmacological antagonists and knockout mice that we used to unravel this sequence of events in rodents. Finally, we describe experiments in mononuclear cells obtained from normotensive or hypertensive volunteers, which confirm that analogous processes of salt-induced immunity take place in humans.

Hypertension: Do Inflammation and Immunity Hold the Key to Solving this Epidemic?

Elevated cardiovascular risk including stroke, heart failure, and heart attack is present even after normalization of blood pressure in patients with hypertension. Underlying immune cell activation is a likely culprit. Although immune cells are important for protection against invading pathogens, their chronic overactivation may lead to tissue damage and high blood pressure. Triggers that may initiate immune activation include viral infections, autoimmunity, and lifestyle factors such as excess dietary salt. These conditions activate the immune system either directly or through their impact on the gut microbiome, which ultimately produces chronic inflammation and hypertension. T cells are central to the immune responses contributing to hypertension. They are activated in part by binding specific antigens that are presented in major histocompatibility complex molecules on professional antigen-presenting cells, and they generate repertoires of rearranged T-cell receptors. Activated T cells infiltrate tissues and produce cytokines including interleukin 17A, which promote renal and vascular dysfunction and end-organ damage leading to hypertension. In this comprehensive review, we highlight environmental, genetic, and microbial associated mechanisms contributing to both innate and adaptive immune cell activation leading to hypertension. Targeting the underlying chronic immune cell activation in hypertension has the potential to mitigate the excess cardiovascular risk associated with this common and deadly disease.