Sodium activates human monocytes via the NADPH oxidase and isolevuglandin formation.

AIMS: Prior studies have focused on the role of the kidney and vasculature in salt-induced modulation of blood pressure; however, recent data indicate that sodium accumulates in tissues and can activate immune cells. We sought to examine mechanisms by which salt causes activation of human monocytes both in vivo and in vitro. METHODS AND RESULTS: To study the effect of salt in human monocytes, monocytes were isolated from volunteers to perform several in vitro experiments. Exposure of human monocytes to elevated Na+ex vivo caused a co-ordinated response involving isolevuglandin (IsoLG)-adduct formation, acquisition of a dendritic cell (DC)-like morphology, expression of activation markers CD83 and CD16, and increased production of pro-inflammatory cytokines tumour necrosis factor-α, interleukin (IL)-6, and IL-1ß. High salt also caused a marked change in monocyte gene expression as detected by RNA sequencing and enhanced monocyte migration to the chemokine CC motif chemokine ligand 5. NADPH-oxidase inhibition attenuated monocyte activation and IsoLG-adduct formation. The increase in IsoLG-adducts correlated with risk factors including body mass index, pulse pressure. Monocytes exposed to high salt stimulated IL-17A production from autologous CD4+ and CD8+ T cells. In addition, to evaluate the effect of salt in vivo, monocytes and T cells isolated from humans were adoptively transferred to immunodeficient NSG mice. Salt feeding of humanized mice caused monocyte-dependent activation of human T cells reflected by proliferation and accumulation of T cells in the bone marrow. Moreover, we performed a cross-sectional study in 70 prehypertensive subjects. Blood was collected for flow cytometric analysis and 23Na magnetic resonance imaging was performed for tissue sodium measurements. Monocytes from humans with high skin Na+ exhibited increased IsoLG-adduct accumulation and CD83 expression. CONCLUSION: Human monocytes exhibit co-ordinated increases in parameters of activation, conversion to a DC-like phenotype and ability to activate T cells upon both in vitro and in vivo sodium exposure. The ability of monocytes to be activated by sodium is related to in vivo cardiovascular disease risk factors. We therefore propose that in addition to the kidney and vasculature, immune cells like monocytes convey salt-induced cardiovascular risk in humans.

Sympathetic Enhancement of Memory T-Cell Homing and Hypertension Sensitization.

RATIONALE: Effector memory T lymphocytes (TEM cells) exacerbate hypertension in response to repeated hypertensive stimuli. These cells reside in the bone marrow for prolonged periods and can be reactivated on reexposure to the hypertensive stimulus. OBJECTIVE: Because hypertension is associated with increased sympathetic outflow to the bone marrow, we hypothesized that sympathetic nerves regulate accumulation and reactivation of bone marrow-residing hypertension-specific TEM cells. METHODS AND RESULTS: Using unilateral superior cervical ganglionectomy in wild-type C57BL/6 mice, we showed that sympathetic nerves create a bone marrow environment that supports residence of hypertension-specific CD8+ T cells. These cells, defined by their proliferative response on coculture with dendritic cells from Ang (angiotensin) II-infused mice, were reduced in denervated compared with innervated bone of Ang II-infused mice. Adoptively transferred CD8+ T cells from Ang II-infused mice preferentially homed to innervated compared with denervated bone. In contrast, ovalbumin responsive T cells from OT-I mice did not exhibit this preferential homing. Increasing superior cervical ganglion activity by activating Gq-coupled designer receptor exclusively activated by designer drug augmented CD8+ TEM bone marrow accumulation. Adoptive transfer studies using mice lacking ß2AR (ß2 adrenergic receptors) indicate that ß2AR in the bone marrow niche, rather than T-cell ß2AR is critical for TEM cell homing. Inhibition of global sympathetic outflow using Gi-coupled DREADD (designer receptor exclusively activated by designer drug) injected into the rostral ventrolateral medulla or treatment with a ß2AR antagonist reduced hypertension-specific CD8+ TEM cells in the bone marrow and reduced the hypertensive response to a subsequent response to low dose Ang II. CONCLUSIONS: Sympathetic nerves contribute to the homing and survival of hypertension-specific TEM cells in the bone marrow after they are formed in hypertension. Inhibition of sympathetic nerve activity and ß2AR blockade reduces these cells and prevents the blood pressure elevation and renal inflammation on reexposure to hypertension stimuli.

Critical role of Interleukin 21 and T follicular helper cells in hypertension and vascular dysfunction.

T and B cells have been implicated in hypertension, but the mechanisms by which they produce a coordinated response is unknown. T follicular helper (Tfh) cells that produce interleukin 21 (IL21) promote germinal center (GC) B cell responses leading to immunoglobulin (Ig) production. Here we investigate the role of IL21 and Tfh cells in hypertension. In response to angiotensin (Ang) II-induced hypertension, T cell IL21 production is increased, and Il21-/- mice develop blunted hypertension, attenuated vascular end-organ damage, and decreased interleukin 17A (IL17A) and interferon gamma production. Tfh-like cells and GC B cells accumulate in the aorta and plasma IgG1 is increased in hypertensive WT but not Il21-/-mice. Furthermore, Tfh cell deficient mice develop blunted hypertension and vascular hypertrophy in response to Ang II infusion. Importantly, IL21 neutralization reduces blood pressure (BP) and reverses endothelial dysfunction and vascular inflammation. Moreover, recombinant IL21 impairs endothelium-dependent relaxation ex vivo and decreases nitric oxide production from cultured endothelial cells. Finally, we show in humans that peripheral blood T cell production of IL21 correlates with systolic BP and IL17A production. These data suggest that IL21 may be a novel therapeutic target for the treatment of hypertension and its micro- and macrovascular complications.

Role of afferent and efferent renal nerves in the development of AngII-salt hypertension in rats.

Hypertension is the leading modifiable risk factor for death worldwide, yet the causes remain unclear and treatment remains suboptimal. Catheter-based renal denervation (RDNX) is a promising new treatment for resistant hypertension, but the mechanisms underlying its antihypertensive effect remain unclear. We recently found that RDNX attenuates deoxycorticosterone acetate-salt hypertension and that this is dependent on ablation of afferent renal nerves and is associated with decreased renal inflammation. To determine if this is common to other models of salt-sensitive hypertension, rats underwent complete RDNX (n = 8), selective ablation of afferent renal nerves (n = 8), or sham denervation (n = 8). Mean arterial pressure (MAP) and heart rate were measure by telemetry and rats were housed in metabolic cages for measurement of sodium and water balance. Rats were then subjected to angiotensin II (AngII)-salt hypertension (10 ng/kg/min, intravenous + 4% NaCl diet) for 2 weeks. At the end of the study, renal T-cell infiltration was quantified by flow cytometry. AngII resulted in an increase in MAP of ~50 mmHg in all three groups with no between group differences, and a transient bradycardia that was blunted by selective ablation of afferent renal nerves. Sodium and water balance were unaffected by AngII-salt treatment and similar between groups. Lastly, AngII infusion was not associated with T-cell infiltration into the kidneys, and T-cell counts were unaffected by the denervation procedures. These results suggest that AngII-salt hypertension in the rat is not associated with renal inflammation and that neither afferent nor efferent renal nerves contribute to this model.

Dendritic Cell Amiloride-Sensitive Channels Mediate Sodium-Induced Inflammation and Hypertension.

Sodium accumulates in the interstitium and promotes inflammation through poorly defined mechanisms. We describe a pathway by which sodium enters dendritic cells (DCs) through amiloride-sensitive channels including the alpha and gamma subunits of the epithelial sodium channel and the sodium hydrogen exchanger 1. This leads to calcium influx via the sodium calcium exchanger, activation of protein kinase C (PKC), phosphorylation of p47phox, and association of p47phox with gp91phox. The assembled NADPH oxidase produces superoxide with subsequent formation of immunogenic isolevuglandin (IsoLG)-protein adducts. DCs activated by excess sodium produce increased interleukin-1ß (IL-1ß) and promote T cell production of cytokines IL-17A and interferon gamma (IFN-γ). When adoptively transferred into naive mice, these DCs prime hypertension in response to a sub-pressor dose of angiotensin II. These findings provide a mechanistic link between salt, inflammation, and hypertension involving increased oxidative stress and IsoLG production in DCs.

Renal Nerves and Long-Term Control of Arterial Pressure.

The objective of this review is to provide an in-depth evaluation of how renal nerves regulate renal and cardiovascular function with a focus on long-term control of arterial pressure. We begin by reviewing the anatomy of renal nerves and then briefly discuss how the activity of renal nerves affects renal function. Current methods for measurement and quantification of efferent renal-nerve activity (ERNA) in animals and humans are discussed. Acute regulation of ERNA by classical neural reflexes as well and hormonal inputs to the brain is reviewed. The role of renal nerves in long-term control of arterial pressure in normotensive and hypertensive animals (and humans) is then reviewed with a focus on studies utilizing continuous long-term monitoring of arterial pressure. This includes a review of the effect of renal-nerve ablation on long-term control of arterial pressure in experimental animals as well as humans with drug-resistant hypertension. The extent to which changes in arterial pressure are due to ablation of renal afferent or efferent nerves are reviewed. We conclude by discussing the importance of renal nerves, relative to sympathetic activity to other vascular beds, in long-term control of arterial pressure and hypertension and propose directions for future research in this field. © 2017 American Physiological Society. Compr Physiol 7:263-320, 2017.

Do high-salt microenvironments drive hypertensive inflammation?

Hypertension is a global epidemic affecting over one billion people worldwide. Despite this, the etiology of most cases of human hypertension remains obscure, and treatment remains suboptimal. Excessive dietary salt and inflammation are known contributors to the pathogenesis of this disease. Recently, it has been recognized that salt can accumulate in the skin and skeletal muscle, producing concentrations of sodium greater than the plasma in hypertensive animals and humans. Such elevated levels of sodium have been shown to alter immune cell function. Here, we propose a model in which tissue salt accumulation causes an immune response leading to renal and vascular inflammation and hypertension.

Resting Afferent Renal Nerve Discharge and Renal Inflammation: Elucidating the Role of Afferent and Efferent Renal Nerves in Deoxycorticosterone Acetate Salt Hypertension.

Renal sympathetic denervation (RDNx) has emerged as a novel therapy for hypertension; however, the therapeutic mechanisms remain unclear. Efferent renal sympathetic nerve activity has recently been implicated in trafficking renal inflammatory immune cells and inflammatory chemokine and cytokine release. Several of these inflammatory mediators are known to activate or sensitize afferent nerves. This study aimed to elucidate the roles of efferent and afferent renal nerves in renal inflammation and hypertension in the deoxycorticosterone acetate (DOCA) salt rat model. Uninephrectomized male Sprague-Dawley rats (275-300 g) underwent afferent-selective RDNx (n=10), total RDNx (n=10), or Sham (n=10) and were instrumented for the measurement of mean arterial pressure and heart rate by radiotelemetry. Rats received 100-mg DOCA (SC) and 0.9% saline for 21 days. Resting afferent renal nerve activity in DOCA and vehicle animals was measured after the treatment protocol. Renal tissue inflammation was assessed by renal cytokine content and T-cell infiltration and activation. Resting afferent renal nerve activity, expressed as a percent of peak afferent nerve activity, was substantially increased in DOCA than in vehicle (35.8±4.4 versus 15.3±2.8 %Amax). The DOCA-Sham hypertension (132±12 mm Hg) was attenuated by ≈50% in both total RDNx (111±8 mm Hg) and afferent-selective RDNx (117±5 mm Hg) groups. Renal inflammation induced by DOCA salt was attenuated by total RDNx and unaffected by afferent-selective RDNx. These data suggest that afferent renal nerve activity may mediate the hypertensive response to DOCA salt, but inflammation may be mediated primarily by efferent renal sympathetic nerve activity. Also, resting afferent renal nerve activity is elevated in DOCA salt rats, which may highlight a crucial neural mechanism in the development and maintenance of hypertension.

CD70 Exacerbates Blood Pressure Elevation and Renal Damage in Response to Repeated Hypertensive Stimuli.

RATIONALE: Accumulating evidence supports a role of adaptive immunity and particularly T cells in the pathogenesis of hypertension. Formation of memory T cells, which requires the costimulatory molecule CD70 on antigen-presenting cells, is a cardinal feature of adaptive immunity. OBJECTIVE: To test the hypothesis that CD70 and immunologic memory contribute to the blood pressure elevation and renal dysfunction mediated by repeated hypertensive challenges. METHODS AND RESULTS: We imposed repeated hypertensive challenges using either N(ω)-nitro-L-arginine methyl ester hydrochloride (L-NAME)/high salt or repeated angiotensin II stimulation in mice. During these challenges effector memory T cells (T(EM)) accumulated in the kidney and bone marrow. In the L-NAME/high-salt model, memory T cells of the kidney were predominant sources of interferon-γ and interleukin-17A, known to contribute to hypertension. L-NAME/high salt increased macrophage and dendritic cell surface expression of CD70 by 3- to 5-fold. Mice lacking CD70 did not accumulate T(EM) cells and did not develop hypertension to either high salt or the second angiotensin II challenge and were protected against renal damage. Bone marrow-residing T(EM) cells proliferated and redistributed to the kidney in response to repeated salt feeding. Adoptively transferred T(EM) cells from hypertensive mice homed to the bone marrow and spleen and expanded on salt feeding of the recipient mice. CONCLUSIONS: Our findings illustrate a previously undefined role of CD70 and long-lived T(EM) cells in the development of blood pressure elevation and end-organ damage that occur on delayed exposure to mild hypertensive stimuli. Interventions to prevent repeated hypertensive surges could attenuate formation of hypertension-specific T(EM) cells.

Differential role of afferent and efferent renal nerves in the maintenance of early- and late-phase Dahl S hypertension.

Clinical data suggest that renal denervation (RDNX) may be an effective treatment for human hypertension; however, it is unclear whether this therapeutic effect is due to ablation of afferent or efferent renal nerves. We have previously shown that RDNX lowers arterial pressure in hypertensive Dahl salt-sensitive (S) rats to a similar degree observed in clinical trials. In addition, we have recently developed a method for selective ablation of afferent renal nerves (renal-CAP). In the present study, we tested the hypothesis that the antihypertensive effect of RDNX in the Dahl S rat is due to ablation of afferent renal nerves by comparing the effect of complete RDNX to renal-CAP during two phases of hypertension in the Dahl S rat. In the early phase, rats underwent treatment after 3 wk of high-NaCl feeding when mean arterial pressure (MAP) was ∼ 140 mmHg. In the late phase, rats underwent treatment after 9 wk of high NaCl feeding, when MAP was ∼ 170 mmHg. RDNX reduced MAP ∼ 10 mmHg compared with sham surgery in both the early and late phase, whereas renal-CAP had no antihypertensive effect. These results suggest that, in the Dahl S rat, the antihypertensive effect of RDNX is not dependent on pretreatment arterial pressure, nor is it due to ablation of afferent renal nerves.

Renal Denervation Prevents Immune Cell Activation and Renal Inflammation in Angiotensin II-Induced Hypertension.

RATIONALE: Inflammation and adaptive immunity play a crucial role in the development of hypertension. Angiotensin II and probably other hypertensive stimuli activate the central nervous system and promote T-cell activation and end-organ damage in peripheral tissues. OBJECTIVE: To determine if renal sympathetic nerves mediate renal inflammation and T-cell activation in hypertension. METHODS AND RESULTS: Bilateral renal denervation using phenol application to the renal arteries reduced renal norepinephrine levels and blunted angiotensin II-induced hypertension. Bilateral renal denervation also reduced inflammation, as reflected by decreased accumulation of total leukocytes, T cells, and both CD4+ and CD8+ T cells in the kidney. This was associated with a marked reduction in renal fibrosis, albuminuria, and nephrinuria. Unilateral renal denervation, which partly attenuated blood pressure, only reduced inflammation in the denervated kidney, suggesting that this effect is pressure independent. Angiotensin II also increased immunogenic isoketal-protein adducts in renal dendritic cells (DCs) and increased surface expression of costimulation markers and production of interleukin (IL)-1α, IL-1ß, and IL-6 from splenic DCs. Norepinephrine also dose dependently stimulated isoketal formation in cultured DCs. Adoptive transfer of splenic DCs from angiotensin II-treated mice primed T-cell activation and hypertension in recipient mice. Renal denervation prevented these effects of hypertension on DCs. In contrast to these beneficial effects of ablating all renal nerves, renal afferent disruption with capsaicin had no effect on blood pressure or renal inflammation. CONCLUSIONS: Renal sympathetic nerves contribute to DC activation, subsequent T-cell infiltration and end-organ damage in the kidney in the development of hypertension.

A novel method of selective ablation of afferent renal nerves by periaxonal application of capsaicin.

Renal denervation has been shown to lower arterial pressure in some hypertensive patients, yet it remains unclear whether this is due to ablation of afferent or efferent renal nerves. To investigate the role of afferent renal nerves in arterial pressure regulation, previous studies have used methods that disrupt both renal and nonrenal afferent signaling. The present study was conducted to develop and validate a technique for selective ablation of afferent renal nerves that does not disrupt other afferent pathways. To do this, we adapted a technique for sensory denervation of the adrenal gland by topical application of capsaicin and tested the hypothesis that exposure of the renal nerves to capsaicin (renal-CAP) causes ablation of afferent but not efferent renal nerves. Renal-CAP had no effect on renal content of the efferent nerve markers tyrosine hydroxylase and norepinephrine; however, the afferent nerve marker, calcitonin gene-related peptide was largely depleted from the kidney 10 days after intervention, but returned to roughly half of control levels by 7 wk postintervention. Moreover, renal-CAP abolished the cardiovascular responses to acute pharmacological stimulation of afferent renal nerves. Renal-CAP rats showed normal weight gain, as well as cardiovascular and fluid balance regulation during dietary sodium loading. To some extent, renal-CAP did blunt the bradycardic response and increase the dipsogenic response to increased salt intake. Lastly, renal-CAP significantly attenuated the development of deoxycorticosterone acetate-salt hypertension. These results demonstrate that renal-CAP effectively causes selective ablation of afferent renal nerves in rats.

Reversal of genetic salt-sensitive hypertension by targeted sympathetic ablation.

The sympathetic nervous system plays an important role in some forms of human hypertension as well as the Dahl salt-sensitive rat model of hypertension; however, the sympathetic targets involved remain unclear. To address this, we examined the role of the renal and splanchnic sympathetic nerves in Dahl hypertension by performing sham surgery (n=10) or targeted sympathetic ablation of the renal nerves (renal denervation, n=11), the splanchnic nerves (celiac ganglionectomy, n=11), or both renal and splanchnic nerves (n=11) in hypertensive Dahl rats. Mean arterial pressure increased from ≈120 mm Hg, while on a 0.1% sodium chloride diet, to ≈140 mm Hg after being fed a 4.0% sodium chloride diet for 3 weeks. At that point, rats underwent sham or targeted sympathetic ablation. Four weeks after treatment, mean arterial pressure was lower in renal denervated (150.4±10.4) and celiac ganglionectomized (147.0±6.1) rats compared with sham rats (165.0±3.7) and even lower in rats that underwent both ablations (128.4±6.6). There were no differences in heart rate or fluid balance between sham and renal denervated rats; however, rats that underwent either celiac ganglionectomy or both ablations exhibited marked tachycardia as well as sodium and water retention after treatment. These data suggest that targeted sympathetic ablation is an effective treatment for established hypertension in the Dahl rat and that the kidneys and the splanchnic vascular bed are both independently important targets of the sympathetic nervous system in this model.