Myeloid Suppressor Cells Accumulate and Regulate Blood Pressure in Hypertension

Advances in Understanding of the Role of Immune Cell Phenotypes in Hypertension and Associated Vascular Disease

Many studies in the past 20 years have identified a contribution of inflammation and immune mechanisms to the pathophysiology of hypertension. Innate and adaptive immunity participate in this process. Among innate immune cells, macrophages and monocytes as well as dendritic cells, myeloid-derived suppressor cells, and neutrophils directly or via formation of neutrophil extracellular traps, play roles in the modulation of the inflammatory response in hypertension. Among adaptive immune cells, T and B cells have been implicated to varying degrees, particularly interleukin (IL)-17- and interferon γ-producing T lymphocytes, antagonized by T regulatory lymphocytes that are anti-inflammatory via production of IL-10. Among T cells that produce abundant IL-17, γδ T cells are unconventional T lymphocytes that are infrequent in the circulation in contrast to the much more abundant circulating αβ T lymphocytes, but are found mostly in tissues, and appear to play a role in triggering and sustaining inflammation in hypertension leading to vascular and renal injury. This review will provide an overview of these different immune cell phenotypes involved in the immune pathophysiology of hypertension and associated vascular disease.

Immune mechanisms in the pathophysiology of hypertension

Hypertension is a leading risk factor for morbidity and mortality worldwide. Despite current anti-hypertensive therapies, most individuals with hypertension fail to achieve adequate blood pressure control. Moreover, even with adequate control, a residual risk of cardiovascular events and associated organ damage remains. These findings suggest that current treatment modalities are not addressing a key element of the underlying pathology. Emerging evidence implicates immune cells as key mediators in the development and progression of hypertension. In this Review, we discuss our current understanding of the diverse roles of innate and adaptive immune cells in hypertension, highlighting key findings from human and rodent studies. We explore mechanisms by which these immune cells promote hypertensive pathophysiology, shedding light on their multifaceted involvement. In addition, we highlight advances in our understanding of autoimmunity, HIV and immune checkpoints that provide valuable insight into mechanisms of chronic and dysregulated inflammation in hypertension.

Endoplasmic Reticulum Stress in Hypertension and Salt Sensitivity of Blood Pressure

PURPOSE OF REVIEW

Hypertension is a principal risk factor for cardiovascular morbidity and mortality, with its severity exacerbated by high sodium intake, particularly in individuals with salt-sensitive blood pressure. However, the mechanisms underlying hypertension and salt sensitivity are only partly understood. Herein, we review potential interactions in hypertension pathophysiology involving the immune system, endoplasmic reticulum (ER) stress, the unfolded protein response (UPR), and proteostasis pathways; identify knowledge gaps; and discuss future directions.

RECENT FINDINGS

Recent advancements by our research group and others reveal interactions within and between adaptive and innate immune responses in hypertension pathophysiology. The salt-immune-hypertension axis is further supported by the discovery of the role of dendritic cells in hypertension, marked by isolevuglandin (IsoLG) formation. Alongside these broadened understandings of immune-mediated salt sensitivity, the contributions of T cells to hypertension have been recently challenged by groups whose findings did not support increased resistance of Rag-1-deficient mice to Ang II infusion. Hypertension has also been linked to ER stress and the UPR. Notably, a holistic approach is needed because the UPR engages in crosstalk with autophagy, the ubiquitin proteasome, and other proteostasis pathways, that may all involve hypertension. There is a critical need for studies to establish cause and effect relationships between ER stress and the UPR in hypertension pathophysiology in humans and to determine whether the immune system and ER stress function mainly to exacerbate or initiate hypertension and target organ injury. This review of recent studies proposes new avenues for future research for targeted therapeutic interventions.

Immune and inflammatory mechanisms in hypertension

Hypertension is a global health problem, with >1.3 billion individuals with high blood pressure worldwide. In this Review, we present an inflammatory paradigm for hypertension, emphasizing the crucial roles of immune cells, cytokines and chemokines in disease initiation and progression. T cells, monocytes, macrophages, dendritic cells, B cells and natural killer cells are all implicated in hypertension. Neoantigens, the NLRP3 inflammasome and increased sympathetic outflow, as well as cytokines (including IL-6, IL-7, IL-15, IL-18 and IL-21) and a high-salt environment, can contribute to immune activation in hypertension. The activated immune cells migrate to target organs such as arteries (especially the perivascular fat and adventitia), kidneys, the heart and the brain, where they release effector cytokines that elevate blood pressure and cause vascular remodelling, renal damage, cardiac hypertrophy, cognitive impairment and dementia. IL-17 secreted by CD4+ T helper 17 cells and γδ T cells, and interferon-γ and tumour necrosis factor secreted by immunosenescent CD8+ T cells, exert crucial effector roles in hypertension, whereas IL-10 and regulatory T cells are protective. Effector mediators impair nitric oxide bioavailability, leading to endothelial dysfunction and increased vascular contractility. Inflammatory effector mediators also alter renal sodium and water balance and promote renal fibrosis. These mechanisms link hypertension with obesity, autoimmunity, periodontitis and COVID-19. A comprehensive understanding of the immune and inflammatory mechanisms of hypertension is crucial for safely and effectively translating the findings to clinical practice.

Adipose c-Jun NH2-terminal kinase promotes angiotensin II-induced and deoxycorticosterone acetate salt-induced hypertension and vascular dysfunction by inhibition of adiponectin production and activation of SGK1 in mice

BACKGROUND

Adipose c-Jun NH2-terminal kinase 1/2 (JNK1/2) is a central mediator involved in the development of obesity and its complications. However, the roles of adipose JNK1/2 in hypertension remain elusive. Here we explored the role of adipose JNK1/2 in hypertension.

METHODS AND RESULTS

The roles of adipose JNK1/2 in hypertension were investigated by evaluating the impact of adipose JNK1/2 inactivation in both angiotensin II (Ang II)-induced and deoxycorticosterone acetate (DOCA) salt-induced hypertensive mice. Specific inactivation of JNK1/2 in adipocytes significantly alleviates Ang II-induced and DOCA salt-induced hypertension and target organ damage in mice. Interestingly, such beneficial effects are also observed in hypertensive mice after oral administration of JNK1/2 inhibitor SP600125. Mechanistically, adipose JNK1/2 acts on adipocytes to reduce the production of adiponectin (APN), then leads to promote serum and glucocorticoid-regulated kinase 1 (SGK1) phosphorylation and increases epithelial Na + channel α-subunit (ENaCα) expression in both renal cells and adipocytes, respectively, finally exacerbates Na + retention. In addition, chronic treatment of recombinant mouse APN significantly augments the beneficial effects of adipose JNK1/2 inactivation in DOCA salt-induced hypertension. By contrast, the blood pressure-lowering effects of adipose JNK1/2 inactivation are abrogated by adenovirus-mediated SGK1 overexpression in Ang II -treated adipose JNK1/2 inactivation mice.

CONCLUSION

Adipose JNK1/2 promotes hypertension and targets organ impairment via fine-tuning the multiorgan crosstalk among adipose tissue, kidney, and blood vessels.

Immune cells and hypertension

Hypertension is one of the leading causes of death due to target organ injury from cardiovascular disease. Although there are many treatments, only one-sixth of hypertensive patients effectively control their blood pressure. Therefore, further understanding the pathogenesis of hypertension is essential for the treatment of hypertension. Much research shows that immune cells play an important role in the pathogenesis of hypertension. Here, we discuss the roles of different immune cells in hypertension. Many immune cells participate in innate and adaptive immune responses, such as monocytes/macrophages, neutrophils, dendritic cells, NK cells, and B and T lymphocytes. Immune cells infiltrate the blood vessels, kidneys, and hearts and cause damage. The mechanism is that immune cells secrete cytokines such as interleukin, interferon, and tumor necrosis factor, which affect the inflammatory reaction, oxidative stress, and kidney sodium water retention, and finally aggravate or reduce the dysfunction, remodeling, and fibrosis of the blood vessel, kidney, and heart to participate in blood pressure regulation. This article reviews the research progress on immune cells and hypertension.

Inflammation Resolution in the Cardiovascular System: Arterial Hypertension, Atherosclerosis, and Ischemic Heart Disease

Significance: Chronic inflammation has emerged as a major underlying cause of many prevalent conditions in the Western world, including cardiovascular diseases. Although targeting inflammation has emerged as a promising avenue by which to treat cardiovascular disease, it is also associated with increased risk of infection. Recent Advances: Though previously assumed to be passive, resolution has now been identified as an active process, mediated by unique immunoresolving mediators and mechanisms designed to terminate acute inflammation and promote tissue repair. Recent work has determined that failures of resolution contribute to chronic inflammation and the progression of human disease. Specifically, failure to produce pro-resolving mediators and the impaired clearance of dead cells from inflamed tissue have been identified as major mechanisms by which resolution fails in disease. Critical Issues: Drawing from a rapidly expanding body of experimental and clinical studies, we review here what is known about the role of inflammation resolution in arterial hypertension, atherosclerosis, myocardial infarction, and ischemic heart disease. For each, we discuss the involvement of specialized pro-resolving mediators and pro-reparative cell types, including T regulatory cells, myeloid-derived suppressor cells, and macrophages. Future Directions: Pro-resolving therapies offer the promise of limiting chronic inflammation without impairing host defense. Therefore, it is imperative to better understand the mechanisms underlying resolution to identify therapeutic targets. Antioxid. Redox Signal. 40, 292-316.

Sodium Homeostasis and Hypertension

PURPOSE OF REVIEW

This review aims to summarize and discuss the relationship between sodium homeostasis and hypertension, including emerging concepts of factors outside cardiovascular and renal systems influencing sodium homeostasis and hypertension.

RECENT FINDINGS

Recent studies support the dose-response association between higher sodium and lower potassium intakes and a higher cardiovascular risk in addition to the dose-response relationship between sodium restriction and blood pressure lowering. The growing body of evidence suggests the role of genetic determinants, immune system, and gut microbiota in sodium homeostasis and hypertension. Although higher sodium and lower potassium intakes increase cardiovascular risk, salt restriction is beneficial only to a certain limit. The immune system contributes to hypertension through pro-inflammatory effects. Sodium can affect the gut microbiome and induce pro-inflammatory and immune responses that contribute to salt-sensitive hypertension.

Myeloid-derived suppressor cells promote the formation of abdominal aortic aneurysms through the IL-3-ICOSL-ICOS axis

Th17 cells are powerful inflammation promoters in the pathogenesis of abdominal aortic aneurysms (AAAs). Myeloid-derived suppressor cells (MDSCs) can promote the differentiation of Th17 cells in chronic inflammatory autoimmune injury. Here, we aim to examine whether MDSCs regulate the differentiation of Th17 cells to participate in the development of AAA. We demonstrated an abnormal accumulation of MDSCs in AAA patients, which was positively associated with Th17 cells. We established angiotensin II-induced apolipoprotein E knockout mice and found the impaired immunosuppressive function of M-MDSCs. After systemic injection of anti-Gr-1 antibody in AAA mice to deplete circulating MDSCs, AAA formation and the differentiation of Th17 cells were abolished, and the overexpression of inducible T-cell costimulator (ICOS) on Th17 cells was reversed accordingly. Regulating the expression of ICOS ligand (ICOSL) on MDSCs affects the differentiation of Th17 cells. The adoptive transfer of ICOSLlowMDSCs in AAA mice inhibited the differentiation of Th17 cells and the development of AAA. Meanwhile, rIL-3 promoted the survival and immunosuppressive dysfunction of MDSCs, upregulated ICOSL expression on MDSCs by inhibiting activation of the PI3K/AKT signaling pathway, and regulated MDSCs to promote the differentiation of Th17 cells via the ICOSL-ICOS axis. An increase in serum IL-3, ICOSL+MDSCs, and ICOS+Th17 cells was detected in AAA patients, and IL-3 levels were positively correlated with the proportion of ICOSL+MDSC cells. In conclusion, we uncovered a pivotal role of MDSCs in promoting the differentiation of Th17 cells through the IL-3-ICOSL-ICOS axis during AAA, providing an important theoretical basis for understanding the pathogenesis of AAA.

The role of myeloid-derived immunosuppressive cells in cardiovascular disease

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous cell population found in the bone marrow, peripheral blood, and tumor tissue. Their role is mainly to inhibit the monitoring function of innate and adaptive immune cells, which leads to the escape of tumor cells and promotes tumor development and metastasis. Moreover, recent studies have found that MDSCs are therapeutic in several autoimmune disorders due to their strong immunosuppressive ability. Additionally, studies have found that MDSCs have an important role in the formation and progression of other cardiovascular diseases, such as atherosclerosis, acute coronary syndrome, and hypertension. In this review, we will discuss the role of MDSCs in the pathogenesis and treatment of cardiovascular disease.

IFN-γ Contributes to the Immune Mechanisms of Hypertension

Hypertension is the leading cause of cardiovascular disease and the primary risk factor for mortality worldwide. For more than half a century, researchers have demonstrated that immunity plays an important role in the development of hypertension; however, the precise mechanisms are still under investigation. The current body of knowledge indicates that proinflammatory cytokines may play an important role in contributing to immune-related pathogenesis of hypertension. Interferon gamma (IFN-γ), in particular, as an important cytokine that modulates immune responses, has been recently identified as a critical regulator of blood pressure by several groups, including us. In this review, we focus on exploring the role of IFN-γ in contributing to the pathogenesis of hypertension, outlining the various immune producers of this cytokine and described signaling mechanisms involved. We demonstrate a key role for IFN-γ in hypertension through global knockout studies and related downstream signaling pathways that IFN-γ production from CD8+ T cell (CD8T) in the kidney promoting CD8T-stimulated salt retention via renal tubule cells, thereby exacerbating hypertension. We discuss potential activators of these T cells described by the current literature and relay a novel hypothesis for activation.

Update on Immune Mechanisms in Hypertension

The contribution of immune cells in the initiation and maintenance of hypertension is undeniable. Several studies have established the association between hypertension, inflammation, and immune cells from the innate and adaptive immune systems. Here, we provide an update to our 2017 American Journal of Hypertension review on the overview of the cellular immune responses involved in hypertension. Further, we discuss the activation of immune cells and their contribution to the pathogenesis of hypertension in different in vivo models. We also highlight existing gaps in the field of hypertension that need attention. The main goal of this review is to provide a knowledge base for translational research to develop therapeutic strategies that can improve cardiovascular health in humans.

Continuous renal replacement therapy attenuates polymorphonuclear myeloid-derived suppressor cell expansion in pediatric severe sepsis

Background

Myeloid-derived suppressor cells (MDSCs) expansion is an important mechanism underlying immunosuppression during sepsis. Though continuous renal replacement therapy (CRRT) may attenuate hyperinflammatory response in sepsis, its role in regulating MDSCs is unknown. The aim of this study was to assess the potential role of CRRT involved in sepsis-induced MDSCs expansion in pediatric sepsis.

Method

The proportion of polymorphonuclear MDSCs (PMN-MDSCs) was detected before CRRT (pre-CRRT), at 24 hours after CRRT (CRRT 1^st day) and on the 7^th day after CRRT (CRRT 7^th day). The correlation analyses were performed to elucidate the relationship of MDSCs with clinical indexes in sepsis.

Results

Totally 22 pediatric patients with sepsis were enrolled [median age 44 (IQR15, 83) months]. PMN-MDSCs were expanded in pediatric sepsis compared with healthy controls (4.30% vs. 0.37%, P=0.04). The proportion of PMN-MDSCs showed a decreased tendency on the CRRT 7^th day compared with that on the CRRT 1^st day in survivors (2.29% vs.5.32%, P = 0.088). There was no significant difference in the proportion of PMN-MDSCs between survivors and non-survivors before CRRT (4.51% vs. 3.33%, P=0.745). The levels of interleukin 6 (IL-6) was decreased on the CRRT 7^th day compared with CRRT 1^st day in survivors. In the subgroups of patients with significantly decreased IL-6 levels after CRRT, the proportion of PMN-MDSCs on the CRRT 7^th day were also significantly decreased compared with that on the CRRT 1^st day (2.21% vs. 6.67%, P = 0.033).

Conclusion

The proportion of PMN-MDSCs was down-regulated on the CRRT 7^th day in survivors with sepsis. The reduced PMN-MDSCs expansion may relate to decreased IL-6 level.

Pathophysiology and genetics of salt-sensitive hypertension

Most hypertensive cases are primary and heavily associated with modifiable risk factors like salt intake. Evidence suggests that even small reductions in salt consumption reduce blood pressure in all age groups. In that regard, the ACC/AHA described a distinct set of individuals who exhibit salt-sensitivity, regardless of their hypertensive status. Data has shown that salt-sensitivity is an independent risk factor for cardiovascular events and mortality. However, despite extensive research, the pathogenesis of salt-sensitive hypertension is still unclear and tremendously challenged by its multifactorial etiology, complicated genetic influences, and the unavailability of a diagnostic tool. So far, the important roles of the renin-angiotensin-aldosterone system, sympathetic nervous system, and immune system in the pathogenesis of salt-sensitive hypertension have been studied. In the first part of this review, we focus on how the systems mentioned above are aberrantly regulated in salt-sensitive hypertension. We follow this with an emphasis on genetic variants in those systems that are associated with and/or increase predisposition to salt-sensitivity in humans.

Quantifying the impact of gut microbiota on inflammation and hypertensive organ damage

AIMS

Hypertension (HTN) can lead to heart and kidney damage. The gut microbiota has been linked to HTN, although it is difficult to estimate its significance due to the variety of other features known to influence HTN. In the present study, we used germ-free (GF) and colonized (COL) littermate mice to quantify the impact of microbial colonization on organ damage in HTN.

METHODS AND RESULTS

Four-week-old male GF C57BL/6J littermates were randomized to remain GF or receive microbial colonization. HTN was induced by subcutaneous infusion with angiotensin (Ang) II (1.44 mg/kg/d) and 1% NaCl in the drinking water; sham-treated mice served as control. Renal damage was exacerbated in GF mice, whereas cardiac damage was more comparable between COL and GF, suggesting that the kidney is more sensitive to microbial influence. Multivariate analysis revealed a larger effect of HTN in GF mice. Serum metabolomics demonstrated that the colonization status influences circulating metabolites relevant to HTN. Importantly, GF mice were deficient in anti-inflammatory fecal short-chain fatty acids (SCFA). Flow cytometry showed that the microbiome has an impact on the induction of anti-hypertensive myeloid-derived suppressor cells and pro-inflammatory Th17 cells in HTN. In vitro inducibility of Th17 cells was significantly higher for cells isolated from GF than conventionally raised mice.

CONCLUSIONS

Microbial colonization status of mice had potent effects on their phenotypic response to a hypertensive stimulus, and the kidney is a highly microbiota-susceptible target organ in HTN. The magnitude of the pathogenic response in GF mice underscores the role of the microbiome in mediating inflammation in HTN.

TRANSLATION PERSPECTIVE

To assess the potential of microbiota-targeted interventions to prevent organ damage in hypertension, an accurate quantification of microbial influence is necessary. We provide evidence that the development of hypertensive organ damage is dependent on colonization status and suggest that a healthy microbiota provides anti-hypertensive immune and metabolic signals to the host. In the absence of normal symbiotic host-microbiome interactions, hypertensive damage to the kidney in particular is exacerbated. We suggest that hypertensive patients experiencing perturbations to the microbiota, which are common in CVD, may be at a greater risk for target-organ damage than those with a healthy microbiome.

The Immune System in Hypertension: a Lost Shaker of Salt 2021 Lewis K. Dahl Memorial Lecture

The seminal observations of Dr Lewis Dahl regarding renal mechanisms of hypertension remain highly relevant in light of more recent experiments showing that immune system dysfunction contributes to hypertension pathogenesis. Dr Dahl established that inappropriate salt retention in the kidney plays a central role via Ohm's Law in permitting blood pressure elevation. Nevertheless, inflammatory cytokines whose expression is induced in the early stages of hypertension can alter renal blood flow and sodium transporter expression and activity to foster renal sodium retention. By elaborating these cytokines and reactive oxygen species, myeloid cells and T lymphocytes can connect systemic inflammatory signals to aberrant kidney functions that allow sustained hypertension. By activating T lymphocytes, antigen-presenting cells such as dendritic cells represent an afferent sensing mechanism triggering T cell activation, cytokine generation, and renal salt and water reabsorption. Manipulating these inflammatory signals to attenuate hypertension without causing prohibitive systemic immunosuppression will pose a challenge, but disrupting actions of inflammatory mediators locally within the kidney may offer a path through which to target immune-mediated mechanisms of hypertension while capitalizing on Dr Dahl's key recognition of the kidney's importance in blood pressure regulation.

Mosaic theory revised: inflammation and salt play central roles in arterial hypertension

The mosaic theory of hypertension was advocated by Irvine Page ~80 years ago and suggested that hypertension resulted from the close interactions of different causes. Increasing evidence indicates that hypertension and hypertensive end-organ damage are not only mediated by the proposed mechanisms that result in hemodynamic injury. Inflammation plays an important role in the pathophysiology and contributes to the deleterious consequences of arterial hypertension. Sodium intake is indispensable for normal body function but can be detrimental when it exceeds dietary requirements. Recent data show that sodium levels also modulate the function of monocytes/macrophages, dendritic cells, and different T-cell subsets. Some of these effects are mediated by changes in the microbiome and metabolome due to high-salt intake. The purpose of this review is to propose a revised and extended version of the mosaic theory by summarizing and integrating recent advances in salt, immunity, and hypertension research. Salt and inflammation are placed in the middle of the mosaic because both factors influence each of the remaining pieces.

Positive effects of selenium supplementation on selenoprotein S expression and cytokine status in a murine model of acute liver injury

BACKGROUND

It is a consensus that selenomethionine (SeMet) can protect liver from damage, but the immune mechanism of SeMet in acute liver injury (ALI) is still unclear. This study aims to investigate the protective effects of SeMet against ALI and to elucidate the possible immune mechanism.

METHODS

Firstly, the role of SeMet in CCl4-induced ALI mice was investigated through survival rate, serum ALT and AST, liver necrosis and apoptosis analysis. The expression and secretion of inflammatory cytokines and chemokines in the liver and serum of CCl4-induced ALI mice were analyzed by qRT-PCR and ELISA. Then the immune cell phenotypes were analyzed by flow cytometry and confocal imaging. In addition, MDSCs depletion, CXCL12/CXCR4 axis blocking and selenoprotein S (SELENOS) knockdown assays were used to reveal the immune mechanism of SeMet.

RESULTS

We found that SeMet prolonged survival rate, decreased the serum ALT and AST, alleviated liver necrosis and inhibited hepatocytes apoptosis. Prospective, SeMet decreased the expression of IL-6 and TNF-α, and increased the expression of IL-10. Interestingly, SeMet decreased the expression of MCP-1, while increased the expression of CXCL12. The immune analysis showed that SeMet decreased the activation of T cells through promoting MDSCs accumulation mediated by CXCL12/CXCR4 axis. Furthermore, SeMet increased SELENOS expression in vivo, and knockdown of SELENOS effectively abolished the protective effect of SeMet during ALI.

CONCLUSION

This study demonstrates that SeMet alleviates CCl4-induced ALI by promoting MDSCs accumulation through SELENOS mediated CXCL12/CXCR4 axis. Therefore, our study infers that selenium intake may be as a new therapeutic option for management of inflammation-mediated liver injury.

Clinical perspectives on the age-related increase of immunosuppressive activity

The aging process is associated with a remodeling of the immune system involving chronic low-grade inflammation and a gradual decline in the function of the immune system. These processes are also called inflammaging and immunosenescence. The age-related immune remodeling is associated with many clinical changes, e.g., risk for cancers and chronic infections increases, whereas the efficiency of vaccination and immunotherapy declines with aging. On the other hand, there is convincing evidence that chronic inflammatory states promote the premature aging process. The inflammation associated with aging or chronic inflammatory conditions stimulates a counteracting immunosuppression which protects tissues from excessive inflammatory injuries but promotes immunosenescence. Immunosuppression is a driving force in tumors and chronic infections and it also induces the tolerance to vaccination and immunotherapies. Immunosuppressive cells, e.g., myeloid-derived suppressor cells (MDSC), regulatory T cells (Treg), and type M2 macrophages, have a crucial role in tumorigenesis and chronic infections as well as in the tolerance to vaccination and immunotherapies. Interestingly, there is substantial evidence that inflammaging is also associated with an increased immunosuppressive activity, e.g., upregulation of immunosuppressive cells and anti-inflammatory cytokines. Given that both the aging and chronic inflammatory states involve the activation of immunosuppression and immunosenescence, this might explain why aging is a risk factor for tumorigenesis and chronic inflammatory states and conversely, chronic inflammatory insults promote the premature aging process in humans.

PM2.5 increases mouse blood pressure by activating toll-like receptor 3

BACKGROUND AND AIMS

Plenty of literature has documented that fine particulate matter (PM2.5) exposure is related to blood pressure (BP) elevation. Vascular dysfunction is the initiation of cardiovascular diseases, such as hypertension. This thesis set out to assess the role of Toll-like receptor 3 (TLR3) in the increase in BP induced by PM2.5.

METHODS

C57BL/6 and TLR3 deficient (TLR3-/-) male mice were randomly allocated to filtered air chamber or real-world inhaled concentrated PM2.5 chamber. BP was evaluated using non-invasive BP recordings. After euthanasia, the aortas and small mesenteric arteries (SMAs) were isolated, and vascular tone was measured using a wire myograph. Leucocytes were detached to assess myeloid-derived suppressor cells using flow cytometry. siRNA transfection was performed to silence TLR3 expression in the human vascular endothelial cells incubated with PM2.5. The gene expression levels of inflammation, adhesion molecules, and oxidative stress in the aortas were assessed by quantitative PCR.

RESULTS

Exposure to PM2.5 increased mouse BP, and TLR3 deficiency protected against PM2.5 exposure-induced BP increase. Additionally, the injury of vascular function in the aortas and SMAs was inhibited in TLR3-/- mice. The intercellular adhesion molecule-1 (ICAM-1) was attenuated in TLR3-/- mice, accompanied by the inhibition of inflammatory and oxidized genes of the aortas, such as F4/80, interleukin-6, interleukin-1 beta, and NADPH oxidase 4. In vitro, the enhanced mRNA expression of genes encoding inflammation, oxidative stress, and ICAM-1 by PM2.5 was inhibited by TLR3 silence as well.

CONCLUSIONS

PM2.5 exposure increased BP via TLR3 activation and impaired vascular function.

[Gut microflora and metabolic syndrome: new insight into the pathogenesis of hypertension]

Emerging evidences indicate that a microbial imbalance (dysbiosis) is linked to several diseases including metabolic cardiovascular diseases. A fecal microbiota transplantation from hypertensive human donor to germ-free mice caused blood pressure elevation. In addition, there is a report demonstrating that angiotensin II-induced hypertension and vascular dysfunction were attenuated in germ-free mice, suggesting that gut microbiome may mediate development of hypertension. Although detailed mechanism by which the dysbiosis induces an increased blood pressure remains unknown, changes in microbiome may modify host immune systems and induce inflammatory dysfunction in cardiovascular system, resulting in dysregulation of blood pressure. Some cohort studies demonstrated an association between a higher abundance of Streptococcaceae spp. and blood pressure. One recent report demonstrated that an increasing number of gram-positive Streptococcus was found in the feces of adult spontaneously hypertensive rats with an increased intestinal permeability. We hypothesized that increased bacterial toxin levels derived from gut Streptococcus may be a factor inducing blood pressure dysregulation. In this review, we discuss the possible role of microbiome in cardiovascular disease, especially hypertension.

Macrophage depletion protects against endothelial dysfunction and cardiac remodeling in angiotensin II hypertensive mice

Objective: Hypertension is associated with a low-grade systemic inflammation in cardiovascular system. Macrophage infiltration may initiate an inflammatory process that contributes to vascular and ventricular remodeling in hypertensive human and mice. The present study investigated the effect of chemical depletion of macrophage using liposome encapsulated clodronate (LEC) on cardiac hypertrophy and remodeling in angiotensin (Ang) II hypertensive mice.Methods: C57BL/6 mice received an Ang II (1.1 mg/kg/day with a minipump) infusion for 2 weeks to induce hypertension. Endothelium-dependent relaxation (ED) was examined by organ bath, hematoxylin and staining and Masson-Trichrome staining were used to evaluate aorta and cardiac hypertrophy and fibrosis.Results: Ang II infusion significantly increased systolic blood pressure (SBP), cardiac hypertrophy and fibrosis, and impaired EDR accompanied by increased macrophage infiltration in the heart. Treatment with LEC significantly lowered Ang II-induced cardiac hypertrophy and fibrosis and cardiac macrophage infiltration, and improved EDR with a mild reduction in SBP. Ang II increased the expression of inflammatory cytokines tumor necross factor alpha and interleukin 1 beta and profibrotic factors transforming growth factor beta 1 and fibronectin in the heart, with was reduced by LEC treatment. Treatment with LEC prevented Ang II-induced the phosphorphorylation of ERK1/2 and c-Jun-N-terminal kinase.Conclusions: Our study suggests that cardiac macrophage may be critical for hypertensive cardiac hypertrophy and remodeling, the underlying mechanisms may involve initial heart inflammation and the activation of hypertrophic MAPKs pathway.

Growth Arrest Specific-6 and Axl Coordinate Inflammation and Hypertension

[Figure: see text].

Innate immunity and clinical hypertension

Emerging evidence has supported a role of inflammation and immunity in the genesis of hypertension. In humans and experimental models of hypertension, cells of the innate and adaptive immune system enter target tissues, including vessels and the kidney, and release powerful mediators including cytokines, matrix metalloproteinases and reactive oxygen species that cause tissue damage, fibrosis and dysfunction. These events augment the blood pressure elevations in hypertension and promote end-organ damage. Factors that activate immune cells include sympathetic outflow, increased sodium within microenvironments where these cells reside, and signals received from the vasculature. In particular, the activated endothelium releases reactive oxygen species and interleukin (IL)-6 which in turn stimulate transformation of monocytes to become antigen presenting cells and produce cytokines like IL-1β and IL-23, which further affect T cell function to produce IL-17A. Genetic deletion or neutralization of these cytokines ameliorates hypertension and end-organ damage. In this review, we will consider in depth features of the hypertensive milieu that lead to these events and consider new treatment approaches to limit the untoward effects of inflammation in hypertension.

Immune mechanisms in arterial hypertension. Recent advances

Increasing evidence indicates that hypertension and hypertensive end-organ damage are not only mediated by hemodynamic injury. Inflammation also plays an important role in the pathophysiology and contributes to the deleterious consequences of this disease. Cells of the innate immune system including monocyte/macrophages and dendritic cells can promote blood pressure elevation via effects mostly on kidney and vascular function. Moreover, convincing evidence shows that T and B cells from the adaptive immune system are involved in hypertension and hypertensive end-organ damage. Skin monocyte/macrophages, regulatory T cells, natural killer T cells, and myeloid-derived suppressor cells have been shown to exert blood pressure controlling effects. Sodium intake is undoubtedly indispensable for normal body function but can be detrimental when taken in excess of dietary requirements. Sodium levels also modulate the function of monocyte/macrophages, dendritic cells, and different T cell subsets. Some of these effects are mediated by changes in the microbiome and metabolome that can be found after high salt intake. Modulation of the immune response can reduce severity of blood pressure elevation and hypertensive end-organ damage in several animal models. The purpose of this review is to briefly summarize recent advances in immunity and hypertension as well as hypertensive end-organ damage.

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.

The Gut Microbiome in Hypertension: Recent Advances and Future Perspectives

The pathogenesis of hypertension is known to involve a diverse range of contributing factors including genetic, environmental, hormonal, hemodynamic and inflammatory forces, to name a few. There is mounting evidence to suggest that the gut microbiome plays an important role in the development and pathogenesis of hypertension. The gastrointestinal tract, which houses the largest compartment of immune cells in the body, represents the intersection of the environment and the host. Accordingly, lifestyle factors shape and are modulated by the microbiome, modifying the risk for hypertensive disease. One well-studied example is the consumption of dietary fibers, which leads to the production of short-chain fatty acids and can contribute to the expansion of anti-inflammatory immune cells, consequently protecting against the progression of hypertension. Dietary interventions such as fasting have also been shown to impact hypertension via the microbiome. Studying the microbiome in hypertensive disease presents a variety of unique challenges to the use of traditional model systems. Integrating microbiome considerations into preclinical research is crucial, and novel strategies to account for reciprocal host-microbiome interactions, such as the wildling mouse model, may provide new opportunities for translation. The intricacies of the role of the microbiome in hypertensive disease is a matter of ongoing research, and there are several technical considerations which should be accounted for moving forward. In this review we provide insights into the host-microbiome interaction and summarize the evidence of its importance in the regulation of blood pressure. Additionally, we provide recommendations for ongoing and future research, such that important insights from the microbiome field at large can be readily integrated in the context of hypertension.

The effect of macrophage-targeted interventions on blood pressure - a systematic review and meta-analysis of preclinical studies

An increasing body of evidence shows a role for macrophages and monocytes (as their precursors) in hypertension, but with conflicting results with regard to whether they are protective or harmful. Therefore, we systematically reviewed the effect of macrophage interventions on blood pressure in animal models, to explore which factors determine the blood pressure increasing vs. decreasing effect. A search in PubMED and EMBASE yielded 9620 records, 26 of which were included. Eighteen studies (involving 22 different experiments (k = 22)) performed macrophage depletion, whereas 12 studies specifically deleted certain macrophage proteins. The blood pressure effects of macrophage depletion were highly various and directed toward both directions, as expected, which could not be reduced to differences in animal species or methods of hypertension induction. Prespecified subgroup analysis did reveal a potential role for the route in which the macrophage-depleting agent is being administrated (intraperitoneal vs intravenous subgroup difference of P = 0.07 (k = 22), or P < 0.001 in studies achieving considerable (ie, >50%) depletion (k = 18)). Along with findings from specific macrophage protein deletion studies-showing that deletion of one single macrophage protein (like TonEBP, endothelin-B, EP₄, NOX-2 and the angiotensin II type 1 receptor) can alter blood pressure responses to hypertensive stimuli-the indication that each route has its specific depletion pattern regarding targeted tissues and macrophage phenotypes suggests a determinative role for these features. These hypothesis-generating results encourage more detailed depletion characterization of each technique by direct experimental comparisons, providing a chance to obtain more knowledge on which macrophages are beneficial versus detrimental in hypertension development.

Clinical Efficacy and Safety of Angiogenesis Inhibitors: Sex Differences and Current Challenges

Vasoactive molecules, such as vascular endothelial growth factor (VEGF) and endothelins, share cytokine-like activities and regulate endothelial cell (EC) growth, migration and inflammation. Some endothelial mediators and their receptors are targets for currently approved angiogenesis inhibitors, drugs that are either monoclonal antibodies raised towards VEGF, or inhibitors of vascular receptor protein kinases and signaling pathways. Pharmacological interference with the protective functions of ECs results in a similar spectrum of adverse effects. Clinically, the most common side effects of VEGF signaling pathway inhibition include an increase in arterial pressure, left ventricular (LV) dysfunction ultimately causing heart failure, and thromboembolic events, including pulmonary embolism, stroke, and myocardial infarction. Sex steroids such as androgens, progestins, and estrogen and their receptors (ERα, ERβ, GPER; PR-A, PR-B; AR) have been identified as important modifiers of angiogenesis, and sex differences have been reported for anti-angiogenic drugs. This review article discusses the current challenges clinicians are facing with regard to angiogenesis inhibitor treatments, including the need to consider sex differences affecting clinical efficacy and safety. We also propose areas for future research taking into account the role of sex hormone receptors and sex chromosomes. Development of new sex-specific drugs with improved target and cell-type selectivity likely will open the way personalized medicine in men and women requiring antiangiogenic therapy and result in reduced adverse effects and improved therapeutic efficacy.

Innate Immune Mechanisms of Arterial Hypertension and Autoimmune Disease

The immune system is indispensable in the development of vascular dysfunction and hypertension. The interplay between immune cells and the vasculature, kidneys, heart, and blood pressure regulating nuclei in the central nervous system results in a complex and closely interwoven relationship of the immune system with arterial hypertension. A better understanding of this interplay is necessary for optimized and individualized antihypertensive therapy. Our review article focuses on innate cells in hypertension and to what extent they impact on development and preservation of elevated blood pressure. Moreover, we address the association of hypertension with chronic autoimmune diseases. The latter are ideally suited to learn about immune-mediated mechanisms in cardiovascular disease leading to high blood pressure.

The role of inflammation in hypertension: novel concepts

Hypertension remains the most important modifiable risk factor for the development of cardiovascular disease. While it is clear that inflammation plays a pivotal role in the development and maintenance of hypertension, several novel discoveries have been made within the past decade that have advanced the field and have provided new mechanistic insights. First, recent studies have identified a central role of sodium-induced immune cell activation in the pathogenesis of hypertension by altering the gut microbiome and formation of products of lipid oxidation known as isolevuglandins. Second, cytokine elaboration by the inflammasome leading to end-organ dysfunction and immune activation has been found to play a role in the genesis of hypertension. Third, novel techniques have identified previously uncharacterized immune cell populations that may play a functional role in these processes. Finally, the role of inflammation in hypertension may be an important mediator of severe COVID-19 infections. In this review, we discuss these recent advances in the study of inflammation and hypertension and highlight topics for future studies.

Macrophage Depletion Improves Endothelial Insulin Resistance and Protects against Cardiovascular Injury in Salt-Sensitive Hypertension

Vascular endothelial insulin signaling is critical for the maintenance of vascular and metabolic homeostasis. We have previously shown that in hypertensive Dahl rats, impaired vascular insulin action is linked to angiotensin II activation of the NFκB inflammatory pathway. Macrophage polarization (M1) has implicated in hypertensive and metabolic diseases. Here, we investigated the effect of macrophage depletion using liposome-encapsulated clodronate (LEC) on endothelial insulin resistance and cardiovascular remodeling in Dahl salt-sensitive (DS) rats. High salt intake (HS) for 5 weeks increased systolic blood pressure (SBP: 192 ± 5 vs. 144 ± 4 mmHg in NS, p < 0.05), aortic and cardiac hypertrophy, cardiac fibrosis, and impaired acetylcholine- and insulin-induced vasorelaxation, accompanied by impaired insulin activation of endothelial nitric oxide synthases (eNOS)/NO signaling. HS rats had a significant increase in CD68 (a monocyte/macrophage marker) expression in the aorta and the heart. LEC reduced SBP (168 ± 5 mmHg, p < 0.05) and cardiovascular injury and improved acetylcholine- and insulin-mediated vasorelaxation and insulin signaling molecules with a reduction in the macrophage infiltration in the aorta and the heart. HS rats also manifested an increase in the aortic expressions of inflammatory cytokines, including the ratio of phosphorylated inhibitory kappa B (Iκb)/Iκb, tumor necrosis factor α, and phosphorylated c-Jun N-terminal kinase (JNK) and oxidative stress, which were reduced in HS/LEC rats. Our results suggest that in salt-sensitive hypertension, macrophage may importantly contribute to endothelial insulin resistance, vascular inflammation, and injury. These findings support the idea that macrophages may be a new target for immunotherapy of vasculopathy in hypertensive and metabolic disorders.

Immune mechanisms of hypertension

Hypertension affects 30% of adults and is the leading risk factor for heart attack and stroke. Traditionally, hypertension has been regarded as a disorder of two systems that are involved in the regulation of salt-water balance and cardiovascular function: the renin-angiotensin-aldosterone system (RAAS) and the sympathetic nervous system (SNS). However, current treatments that aim to limit the influence of the RAAS or SNS on blood pressure fail in ~40% of cases, which suggests that other mechanisms must be involved. This Review summarizes the clinical and experimental evidence supporting a contribution of immune mechanisms to the development of hypertension. In this context, we highlight the immune cell subsets that are postulated to either promote or protect against hypertension through modulation of cardiac output and/or peripheral vascular resistance. We conclude with an appraisal of knowledge gaps still to be addressed before immunomodulatory therapies might be applied to at least a subset of patients with hypertension.

Immune mechanisms of salt-sensitive hypertension and renal end-organ damage

Immune mechanisms have been recognized to have a role in the pathogenesis of hypertension, vascular disease and kidney damage in humans and animals for many decades. Contemporary advances in experimentation have permitted a deeper understanding of the mechanisms by which inflammation and immunity participate in cardiovascular disease, and multiple observations have demonstrated strong correlations between the discoveries made in animals and those made in patients with hypertension. Of note, striking phenotypic similarities have been observed in the infiltration of immune cells in the kidney and the development of end-organ damage in patients and animal models with sodium-sensitive hypertension. The available data suggest that an initial salt-induced increase in renal perfusion pressure, which is likely independent of immune mechanisms, induces the infiltration of immune cells into the kidney. The mechanisms mediating immune cell infiltration in the kidney are not well understood but likely involve tissue damage, the direct influence of salt to stimulate immune cell activation, sympathetic nerve stimulation or other factors. The infiltrating cells then release cytokines, free radicals and other factors that contribute to renal damage as well as increased retention of sodium and water and vascular resistance, which lead to the further development of hypertension.

Association of Neutrophil-to-Lymphocyte Ratio With Mortality and Cardiovascular Disease in the Jackson Heart Study and Modification by the Duffy Antigen Variant

Importance

The neutrophil-to-lymphocyte ratio (NLR) is associated with mortality and cardiovascular disease at the time of incident disease, but it is not known whether this is true in prospective studies. Further, a common genetic variant of African origin associated with a relative neutropenia, the Duffy antigen variant, is a candidate to modify associations between NLR and outcomes.

Objective

To investigate the association between NLR and mortality and cardiovascular-related outcomes in the Jackson Heart Study (JHS) and validated our findings in the Normative Aging Study (NAS). We also evaluated whether the Duffy antigen variant modifies these associations in the JHS.

Design, Setting, and Participants

The JHS is a large prospective cohort study designed to examine risk factors and cardiovascular disease among African American individuals residing in Jackson, Mississippi. The NAS is a longitudinal cohort established by the United States Department of Veterans Affairs in 1963. The JHS is a population-based longitudinal study. The NAS is an interdisciplinary longitudinal study located in the Veterans Affairs Outpatient Clinic in Boston, Massachusetts. A total of 5301 participants were recruited for the JHS at baseline. Genotype data on the Duffy antigen variant were available in the JHS. The participants in the NAS were white men only and free of chronic disease at the time of recruitment and were invited for in-person examinations every 3 years since 1986. Data were analyzed between November 2016 and January 2018.

Main Outcomes and Measures

All-cause mortality, coronary heart disease (CHD), stroke, and heart failure (HF). Two NLR cutoff values (≥2.15 for overall and ≥1.77 for African American participants) were used as the exposure measurements.

Results

The participants were African American men and women, aged 21 to 93 years, residing in Jackson, Mississippi. For NLR <2.15, the mean age was 54.2 (12.5); for NLR >2.15, the mean age was 56.5 (13.8); for NLR <1.77, the mean age is 54.1 (12.4); and for NLR >1.77, the mean age was 55.8 (13.6). Adjusting for potential confounders, elevated NLR (≥2.15) was significantly associated with an increased risk for all-cause mortality (hazard ratio, 1.40; 95% CI, 1.14-1.70) and CHD (hazard ratio, 1.69; 95% CI, 1.23-2.34) in JHS. Using a lower NLR cutoff (≥1.77) for African American participants did not alter the significant associations. In the NAS, elevated NLR was associated with an increased risk of mortality (hazard ratio, 1.32; 95% CI, 0.99-1.76), with no statistical significance. In both prospective studies, NLR was less of a robust predictor when the time of event was more distant. The Duffy antigen variant was associated with neutrophil count, and NLR (≥1.77) was significantly associated with mortality, CHD, stroke, and HF in the Duffy antigen-negative group.

Conclusions and Relevance

Neutrophil-to-lymphocyte ratio was prospectively associated with all-cause mortality, CHD, and HF, with closer median time to event diagnoses in the JHS. Furthermore, the Duffy antigen variant locus was associated with a lower baseline NLR and modified the mortality, CHD, stroke, and HF associations.

Microglia, autonomic nervous system, immunity and hypertension: Is there a link?

Hypertension ranks the most common risk factor for cardiovascular diseases, and it affects almost one third of adult population globally. Emerging evidence indicates that immune activation is highly involved in the entire progress of hypertension and end organ damage. In addition to immunity, autonomic nervous system, particularly sympathetic nervous system, is one of the most conserved systems to maintain body homeostasis. Immune and sympathetic activities are found simultaneously increased in hypertension, suggesting a synergistic action of these two systems in the progression of this disease. Microglia, the primary immune cells in the central nervous system, have been suggested in the regulation of sympathetic outflow; depletion of microglia alters neuroinflammation and pressor responses in hypertensive models. In this review, we firstly updated the current understanding on microglial ontogeny and functions in both steady state and diseases. Then we reviewed on the interaction between autonomic nervous system and peripheral immunity in hypertension. Microglia bridge the central and peripheral inflammation via regulating the sympathetic nerve activity in hypertension. Future exploration of the molecular linkage of this pathway may provide novel therapeutic angel for hypertension and related cardiovascular diseases.

Adaptive Immunity in Hypertension

PURPOSE OF REVIEW

In recent years, a vast body of evidence has accumulated indicating the role of the immune system in the regulation of blood pressure and modulation of hypertensive pathology. Numerous cells of the immune system, both innate and adaptive immunity, have been indicated to play an important role in the development and maintenance of hypertension. The purpose of this review was to summarize the role of adaptive immunity in experimental models of hypertension (genetic, salt-sensitive, and Angiotensin (Ang) II induced) and in human studies. In particular, the role of T and B cells is discussed.

RECENT FINDINGS

In response to hypertensive stimuli such as Ang II and high salt, T cells become pro-inflammatory and they infiltrate the brain, blood vessel adventitia and periadventitial fat, heart, and the kidney. Pro-inflammatory T cell-derived cytokines such as IFN-γ and TNF-α (from CD8+ and CD4+Th1) and IL-17A (from the γδ-T cell and CD4+Th17) exacerbate hypertensive responses mediating both endothelial dysfunction and cardiac, renal, and neurodegenerative injury. The modulation of adaptive immune activation in hypertension has been attributed to target organ oxidative stress that leads to the generation of neoantigens, including isolevuglandin-modified proteins. The role of adaptive immunity is sex-specific with much more pronounced mechanisms in males than that in females. Hypertension is also associated with B cell activation and production of autoantibodies (anti-Hsp70, anti-Hsp65, anti-Hsp60, anti-AT1R, anti-α1AR, and anti-β1AR). The hypertensive responses can be inhibited by T regulatory lymphocytes (Tregs) and their anti-inflammatory IL-10. Adaptive immunity and its interface with innate mechanisms may represent valuable targets in the modulation of blood pressure, as well as hypertension-related residual risk.

The role of sodium in modulating immune cell function

Sodium intake is undoubtedly indispensable for normal body functions but can be detrimental when taken in excess of dietary requirements. The consequences of excessive salt intake are becoming increasingly clear as high salt consumption persists across the globe. Salt has long been suspected to promote the development of hypertension and cardiovascular diseases and is now also recognized as a potential modulator of inflammatory and autoimmune diseases through its direct and indirect effects on immune cells. The finding that, in addition to the kidneys, other organs such as the skin regulate sodium levels in the body prompted new hypotheses, including the concept that skin-resident macrophages might participate in tissue sodium regulation through their interactions with lymphatic vessels. Moreover, immune cells such as macrophages and different T cell subsets are found in sodium-rich interstitial microenvironments, where sodium levels modulate their function. Alterations to the intestinal bacterial community induced by excess dietary salt represent another relevant axis whereby salt indirectly modulates immune cell function. Depending on the inflammatory context, sodium might either contribute to protective immunity (for example, by enhancing host responses against cutaneous pathogens) or it might contribute to immune dysregulation and promote the development of cardiovascular and autoimmune diseases.

High Salt Inhibits Tumor Growth by Enhancing Anti-tumor Immunity

Excess salt intake could affect the immune system by shifting the immune cell balance toward a pro-inflammatory state. Since this shift of the immune balance is thought to be beneficial in anti-cancer immunity, we tested the impact of high salt diets on tumor growth in mice. Here we show that high salt significantly inhibited tumor growth in two independent murine tumor transplantation models. Although high salt fed tumor-bearing mice showed alterations in T cell populations, the effect seemed to be largely independent of adaptive immune cells. In contrast, depletion of myeloid-derived suppressor cells (MDSCs) significantly reverted the inhibitory effect on tumor growth. In line with this, high salt conditions almost completely blocked murine MDSC function in vitro. Importantly, similar effects were observed in human MDSCs isolated from cancer patients. Thus, high salt conditions seem to inhibit tumor growth by enabling more pronounced anti-tumor immunity through the functional modulation of MDSCs. Our findings might have critical relevance for cancer immunotherapy.

The effect of diet on hypertensive pathology: is there a link via gut microbiota-driven immunometabolism?

Over the past decade, the immune system has emerged as an important component in the aetiology of hypertension. There has been a blooming interest in the contribution of the gut microbiota, the microbes that inhabit our small and large intestine, to blood pressure (BP) regulation. The gastrointestinal tract houses the largest number of immune cells in our body, thus, it is no surprise that its microbiota plays an important functional role in the appropriate development of the immune system through a co-ordinated sequence of events leading to immune tolerance of commensal bacteria. Importantly, recent evidence supports that the gut microbiota can protect or promote the development of experimental hypertension and is likely to have a role in human hypertension. One of the major modulators of the gut microbiota is diet: diets that emphasize high intake of fermentable fibre, such as the Mediterranean diet and the Dietary Approaches to Stop Hypertension, promote expansion of protective microbes that release gut metabolites such as short-chain fatty acids, which are immune-, BP-, and cardio-protective, likely acting through G-coupled protein receptors. In contrast, diets lacking fibre or high in salt and fat, such as the Western diet, reduce prevalence of commensal microbial species and support a pathogenic and pro-inflammatory environment, including the release of the pro-atherosclerotic trimethylamine N-oxide. Here, we review the current understanding of the gut microbiota-driven immune dysfunction in both experimental and clinical hypertension, and how these changes may be addressed through dietary interventions.

Sodium in the microenvironment regulates immune responses and tissue homeostasis

During tissue inflammation, immune cells infiltrate the interstitial space of target organs, where they sense and adapt to local environmental stimuli. Such stimuli include not only pathogens but also local factors such as the levels of oxygenation, nutrients and electrolytes. An important electrolyte in this regard is sodium (Na+). Recent in vivo findings have shown a role of Na+ storage in the skin for electrolyte homeostasis. Thereby, Na+ intake may influence the activation status of the immune system through direct effects on T helper cell subsets and innate immune cells in tissues such as the skin and other target organs. Furthermore, high Na+ intake has been shown to alter the composition of the intestinal microbiota, with indirect effects on immune cells. The results suggest regulatory roles for Na+ in cardiovascular disease, inflammation, infection and autoimmunity.

Overexpression of the C-domain of angiotensin-converting enzyme reduces melanoma growth by stimulating M1 macrophage polarization

Angiotensin-converting enzyme (ACE) can hydrolyze many peptides and plays a central role in controlling blood pressure. Moreover, ACE overexpression in monocytes and macrophages increases resistance of mice to tumor growth. ACE is composed of two independent catalytic domains. Here, to investigate the specific role of each domain in tumor resistance, we overexpressed either WT ACE (Tg-ACE mice) or ACE lacking N- or C-domain catalytic activity (Tg-NKO and Tg-CKO mice) in the myeloid cells of mice. Tg-ACE and Tg-NKO mice exhibited strongly suppressed growth of B16-F10 melanoma because of increased ACE expression in macrophages, whereas Tg-CKO mice resisted melanoma no better than WT animals. The effect of ACE overexpression reverted to that of the WT enzyme with an ACE inhibitor but not with an angiotensin II type 1 (AT1) receptor antagonist. ACE C-domain overexpression in macrophages drove them toward a pronounced M1 phenotype upon tumor stimulation, with increased activation of NF-κB and signal transducer and activator of transcription 1 (STAT1) and decreased STAT3 and STAT6 activation. Tumor necrosis factor α (TNFα) is important for M1 activation, and TNFα blockade reverted Tg-NKO macrophages to a WT phenotype. Increased ACE C-domain expression increased the levels of reactive oxygen species (ROS) and of the transcription factor C/EBPβ in macrophages, important stimuli for TNFα expression, and decreased expression of several M2 markers, including interleukin-4Rα. Natural ACE C-domain-specific substrates are not well-described, and we propose that the peptide(s) responsible for the striking ACE-mediated enhancement of myeloid function are substrates/products of the ACE C-domain.

Angiotensin II Signal Transduction: An Update on Mechanisms of Physiology and Pathophysiology

The renin-angiotensin-aldosterone system plays crucial roles in cardiovascular physiology and pathophysiology. However, many of the signaling mechanisms have been unclear. The angiotensin II (ANG II) type 1 receptor (AT₁R) is believed to mediate most functions of ANG II in the system. AT₁R utilizes various signal transduction cascades causing hypertension, cardiovascular remodeling, and end organ damage. Moreover, functional cross-talk between AT₁R signaling pathways and other signaling pathways have been recognized. Accumulating evidence reveals the complexity of ANG II signal transduction in pathophysiology of the vasculature, heart, kidney, and brain, as well as several pathophysiological features, including inflammation, metabolic dysfunction, and aging. In this review, we provide a comprehensive update of the ANG II receptor signaling events and their functional significances for potential translation into therapeutic strategies. AT₁R remains central to the system in mediating physiological and pathophysiological functions of ANG II, and participation of specific signaling pathways becomes much clearer. There are still certain limitations and many controversies, and several noteworthy new concepts require further support. However, it is expected that rigorous translational research of the ANG II signaling pathways including those in large animals and humans will contribute to establishing effective new therapies against various diseases.

Role of immune cells in hypertension

Inflammatory processes have been shown to play an important role in the mechanisms involved in the pathogenesis of hypertension. Innate and adaptive immune responses participate in BP elevation and end-organ damage. Here, we discuss recent studies focusing on novel inflammatory and immune mechanisms that play roles in BP elevation. Different subpopulations of cells involved in innate and adaptive immune responses, such as dendritic cells, monocytes/macrophages and NK cells, on the one hand, and B and T lymphocytes, on the other, contribute to the vascular and kidney injury in hypertension. Unconventional innate-like T cells such as γδ T cells also participate in hypertensive mechanisms by priming both innate and adaptive immune cells, contributing to trigger vascular inflammation and BP elevation. These cells exert their effects in part via production of various cytokines including pro-inflammatory IFN-γ and IL-17 and anti-inflammatory IL-10. The present review summarizes some of these immune mechanisms that participate in the pathophysiology of hypertension. LINKED ARTICLES: This article is part of a themed section on Immune Targets in Hypertension. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.12/issuetoc.

Exclusive enteral nutrition protects against inflammatory bowel disease by inhibiting NF‑κB activation through regulation of the p38/MSK1 pathway

Although enteral nutrition therapy for inflammatory bowel disease has been confirmed to be an effective treatment method, the exact mechanism responsible for the effects of enteral nutrition remains unclear. The aim of the present study was to investigate the protective effect of exclusive enteral nutrition (EEN) against colitis, and to elucidate the potential mechanisms by inhibiting p65 activation via regulating the p38/mitogen‑ and stress‑activated protein kinase‑1 (MSK1) pathway. Experiments were performed by establishing dextran sulfate sodium (DSS)‑mice colitis and picrylsulfonic acid solution (TNBS)‑induced rat colitis, and the results demonstrated that EEN treatment attenuated body weight loss, colon length shortening and colonic pathological damage caused by colitis. EEN also inhibited inflammatory cells infiltration and decreased myeloperoxidase and inducible nitric oxide synthase activities. Furthermore, EEN significantly reduced the production of pro‑inflammatory mediators in serum and the colon. Mechanically, EEN suppressed activation of p65 by inhibiting the p38/MSK1 pathway. In conclusion, the present study demonstrated that EEN attenuated DSS‑ and TNBS‑induced colitis by inhibiting p65 activation via regulating the p38/MSK1 pathway, thus suggesting that EEN is effective in the treatment of colitis.

Inhibition of pregnancy-associated granulocytic myeloid-derived suppressor cell expansion and arginase-1 production in preeclampsia

Myeloid-derived suppressor cells (MDSCs) expand in maternal peripheral blood and cord blood during normal pregnancy to maintain maternal-fetal tolerance. Here we investigated the expansion and function of MDSCs in preeclampsia (PE) patients. Maternal peripheral blood mononuclear cells (PBMCs) and cord blood mononuclear cells (CBMCs) were sampled from healthy pregnant women and PE patients, and analyzed for the frequencies and phenotypes of MDSCs and T cells. Serum levels of key human MDSC effector enzymes were measured using appropriate detection kits. Peripheral blood samples of healthy non-pregnant women were used as controls. We found that normal pregnancy is associated with a significant increase of immunosuppressive MDSCs and regulatory T (Treg) cells. There was no significant difference in the frequency of Treg cells between normal pregnancies and PE patients, but the pregnancy-associated increase of granulocytic MDSCs (G-MDSCs), but not monocytic MDSCs (M-MDSCs), in both PBMCs and CBMCs was markedly inhibited in PE patients. Furthermore, serum levels of Arg-1, an important effector molecule for G-MDSC were significantly reduced in PE patients compared to healthy pregnant women. In conclusion, the lack of G-MDSC expansion is a most notable feature of PE-associated immune-cell alterations, suggesting that restoring G-MDSCs may have the potential to treat PE.

Macrophage Depletion Lowered Blood Pressure and Attenuated Hypertensive Renal Injury and Fibrosis

Monocyte/macrophage recruitment is closely associated with the degree of hypertensive renal injury. We investigated the direct role of macrophages using liposome-encapsulated clodronate (LEC) to deplete monocytes/macrophages in hypertensive renal injury. C57BL/6 mice were treated with a pressor dose of angiotensin (Ang, 1.4 mg/kg/day) II plus LEC or the PBS-liposome for 2 weeks. Ang II mice developed hypertension, albuminuria, glomerulosclerosis, and renal fibrosis. LEC treatment reduced systolic blood pressure (SBP), albuminuria, and protected against renal structural injury in Ang II mice. Ang II significantly increased renal macrophage infiltration (MOMA2⁺ cells) and the expression of renal tumor necrosis factor α and interleukin β1, which were significantly reduced in Ang II/LEC mice. Ang II increased renal oxidative stress and the expression of profibrotic factors transforming growth factor (TGF) β1 and fibronectin. Ang II also inhibited the phosphorylation of endothelial nitric oxide synthase [phospho-endothelial nitric oxide synthesis (eNOS), ser1177]. LEC treatment reduced renal oxidative stress and TGFβ1 and fibronectin expressions, and increased phospho-eNOS expression in the Ang II mice. In Dahl rats of salt-sensitive hypertension, LEC treatment for 4 weeks significantly attenuated the elevation of SBP induced by high salt intake and protected against renal injury and fibrosis. Our results demonstrate that renal macrophages play a critical role in the development of hypertension and hypertensive renal injury and fibrosis; the underlying mechanisms may be involved in the reduction in macrophage-driven renal inflammation and restoration of the balance between renal oxidative stress and eNOS. Therefore, macrophages should be considered as a potential therapeutic target to reduce the adverse consequences of hypertensive renal diseases.