Greater T Regulatory Cells in Females Attenuate DOCA-Salt-Induced Increases in Blood Pressure Versus Males

The role of T cells in vascular aging, hypertension, and atherosclerosis

Vascular dysfunction has emerged as a significant risk factor for the development of cardio- and cerebrovascular diseases (CVDs), which are currently the leading cause of morbidity and mortality worldwide. T lymphocytes (T cells) have been shown to be important modulators of vascular function in primary aging and CVDs, likely by producing inflammatory cytokines and reactive oxygen species that influence vasoprotective molecules. This review summarizes the role of T cells on vascular function in aging, hypertension, and atherosclerosis in animals and humans, and discusses potential T-cell targeted therapeutics to prevent, delay, or reverse vascular dysfunction.

Recent advancements in targeting the immune system to treat hypertension

Hypertension is the key leading risk factor for death globally, affecting ∼1.3 billion adults, particularly in low- and middle-income countries. Most people living with hypertension have uncontrolled high blood pressure, increasing their likelihood of cardiovascular events. Significant issues preventing blood pressure control include lack of diagnosis, treatment, and response to existing therapy. For example, monotherapy and combination therapy are often unable to lower blood pressure to target levels. New therapies are urgently required to tackle this issue, particularly those that target the mechanisms behind hypertension instead of treating its symptoms. Acting via an increase in systemic and tissue-specific inflammation, the immune system is a critical contributor to blood pressure regulation and is considered an early mechanism leading to hypertension development. Here, we review the immune system's role in hypertension, evaluate clinical trials that target inflammation, and discuss knowledge gaps in pre-clinical and clinical data. We examine the effects of anti-inflammatory drugs colchicine and methotrexate on hypertension and evaluate the blockade of pro-inflammatory cytokines IL-1β and TNF-α on blood pressure in clinical trials. Lastly, we highlight how we can move forward to target specific components of the immune system to lower blood pressure. This includes targeting isolevuglandins, which accumulate in dendritic cells to promote T cell activation and cytokine production in salt-induced hypertension. We discuss the potential of the dietary fibre-derived metabolites short-chain fatty acids, which have anti-inflammatory and blood pressure-lowering effects via the gut microbiome. This would limit adverse events, leading to improved medication adherence and better blood pressure control.

The impact of salt consumption on cardiometabolic and cognitive health in aged female rats

Health concerns about excess dietary salt have traditionally focused on its relationship with hypertension and the increased risk of cognitive impairment. However, research has often overlooked the unique health concerns and physiological differences between men and women, leading to gaps in knowledge, particularly regarding disease prevention and treatment strategies for women. The present study examined aged female rats over 12 weeks, using control, low, and high salt diets to mimic the post-menopausal phase in human females when cardiovascular risks typically increase. Cardiometabolic parameters and cognition were monitored. The findings revealed the impact of varying salt diets on blood lipids, blood pressure (BP) and heart rate (HR) levels and variability, anxiety, and cognition. Specifically, intake of a low-salt diet led to a significant reduction in BP levels but an increase in BP variability starting from the eighth week of the diet onset. Moreover, HR levels and variability were notably higher with the low-salt diet. Aged female rats exhibited increased anxiety on the low-salt diet at the fourth week, but the anxiety began to improve starting from the eighth week. Additionally, a trend suggested that the low salt intake worsened short-term memory while improving long-term memory. Furthermore, plasma lipids decreased significantly in aged female rats on a high-salt diet compared to those on a low-salt diet. The study provides valuable insights into the effects of salt intake on cardiometabolic parameters and cognitive function in aged female rats, highlighting the importance of considering sex-specific dietary guidelines for cardiometabolic and cognitive health.

Revisiting sex as a biological variable in hypertension research

Half of adults in the United States have hypertension as defined by clinical practice guidelines. Interestingly, women are generally more likely to be aware of their hypertension and have their blood pressure controlled with treatment compared with men, yet hypertension-related mortality is greater in women. This may reflect the fact that the female sex remains underrepresented in clinical and basic science studies investigating the effectiveness of therapies and the mechanisms controlling blood pressure. This Review provides an overview of the impact of the way hypertension research has explored sex as a biological variable (SABV). Emphasis is placed on epidemiological studies, hypertension clinical trials, the genetics of hypertension, sex differences in immunology and gut microbiota in hypertension, and the effect of sex on the central control of blood pressure. The goal is to offer historical perspective on SABV in hypertension, highlight recent studies that include SABV, and identify key gaps in SABV inclusion and questions that remain in the field. Through continued awareness campaigns and engagement/education at the level of funding agencies, individual investigators, and in the editorial peer review system, investigation of SABV in the field of hypertension research will ultimately lead to improved clinical outcomes.

Sex-Dependency of T Cell-Induced Salt-Sensitive Hypertension and Kidney Damage

BACKGROUND

It is established that the immune system, namely T cells, plays a role in the development of hypertension and renal damage in male Dahl salt-sensitive (SS) rats, but far less is known about this relationship in females. Rats with genetically deleted T cells via CD247 gene mutation on the Dahl SS background (SSCD247-/-) were utilized to interrogate the effect of sex and T cells on salt sensitivity.

METHODS

We assessed the hypertensive and kidney injury phenotypes in male versus female SS and SSCD247-/- rats challenged with 3 weeks of high salt (4.0% NaCl). Differences in T cell activation genes were examined in renal T cells from male and female SS rats, and a sex-specific adoptive transfer was performed by injecting male or female splenocytes into either male or female SSCD247-/- recipients to determine the potential contribution of T cell sex.

RESULTS

The lack of functional T cells in SSCD247-/- rats significantly reduced salt-induced hypertension and proteinuria in both sexes, although SSCD247-/- females exhibited greater protection from kidney damage. Adoptive transfer of either Dahl SS male or female splenocytes into SSCD247-/- male recipients exacerbated hypertension and proteinuria compared with controls, while in SSCD247-/- female recipients, exacerbation of disease occurred only upon transfer of male, but not female, SS splenocytes.

CONCLUSIONS

The absence of T cells in the SSCD247-/- normalized sex differences in blood pressure, though sex differences in renal damage persisted. Splenocyte transfer experiments demonstrated that salt sensitivity is amplified if the sex of the T cell or the recipient is male.

CD4+ T-Cell Legumain Deficiency Attenuates Hypertensive Damage via Preservation of TRAF6

BACKGROUND

T cells are central to the immune responses contributing to hypertension. LGMN (legumain) is highly expressed in T cells; however, its role in the pathogenesis of hypertension remains unclear.

METHODS

Peripheral blood samples were collected from patients with hypertension, and cluster of differentiation (CD)4+ T cells were sorted for gene expression and Western blotting analysis. TLGMNKO (T cell-specific LGMN-knockout) mice (Lgmnf/f/CD4Cre), regulatory T cell (Treg)-specific LGMN-knockout mice (Lgmnf/f/Foxp3YFP Cre), and RR-11a (LGMN inhibitor)-treated C57BL/6 mice were infused with Ang II (angiotensin II) or deoxycorticosterone acetate/salt to establish hypertensive animal models. Flow cytometry, 4-dimensional label-free proteomics, coimmunoprecipitation, Treg suppression, and in vivo Treg depletion or adoptive transfer were used to delineate the functional importance of T-cell LGMN in hypertension development.

RESULTS

LGMN mRNA expression was increased in CD4+ T cells isolated from hypertensive patients and mice, was positively correlated with both systolic and diastolic blood pressure, and was negatively correlated with serum IL (interleukin)-10 levels. TLGMNKO mice exhibited reduced Ang II-induced or deoxycorticosterone acetate/salt-induced hypertension and target organ damage relative to wild-type (WT) mice. Genetic and pharmacological inhibition of LGMN blocked Ang II-induced or deoxycorticosterone acetate/salt-induced immunoinhibitory Treg reduction in the kidneys and blood. Anti-CD25 antibody depletion of Tregs abolished the protective effects against Ang II-induced hypertension in TLGMNKO mice, and LGMN deletion in Tregs prevented Ang II-induced hypertension in mice. Mechanistically, endogenous LGMN impaired Treg differentiation and function by directly interacting with and facilitating the degradation of TRAF6 (tumor necrosis factor receptor-associated factor 6) via chaperone-mediated autophagy, thereby inhibiting NF-κB (nuclear factor kappa B) activation. Adoptive transfer of LGMN-deficient Tregs reversed Ang II-induced hypertension, whereas depletion of TRAF6 in LGMN-deficient Tregs blocked the protective effects.

CONCLUSIONS

LGMN deficiency in T cells prevents hypertension and its complications by promoting Treg differentiation and function. Specifically targeting LGMN in Tregs may be an innovative approach for hypertension treatment.

Sex differences in blood pressure regulation and hypertension: renal, hemodynamic, and hormonal mechanisms

The teleology of sex differences has been argued since at least as early as Aristotle's controversial Generation of Animals more than 300 years BC, which reflects the sex bias of the time to contemporary readers. Although the question "why are the sexes different" remains a topic of debate in the present day in metaphysics, the recent emphasis on sex comparison in research studies has led to the question "how are the sexes different" being addressed in health science through numerous observational studies in both health and disease susceptibility, including blood pressure regulation and hypertension. These efforts have resulted in better understanding of differences in males and females at the molecular level that partially explain their differences in vascular function and renal sodium handling and hence blood pressure and the consequential cardiovascular and kidney disease risks in hypertension. This review focuses on clinical studies comparing differences between men and women in blood pressure over the life span and response to dietary sodium and highlights experimental models investigating sexual dimorphism in the renin-angiotensin-aldosterone, vascular, sympathetic nervous, and immune systems, endothelin, the major renal sodium transporters/exchangers/channels, and the impact of sex hormones on these systems in blood pressure homeostasis. Understanding the mechanisms governing sex differences in blood pressure regulation could guide novel therapeutic approaches in a sex-specific manner to lower cardiovascular risks in hypertension and advance personalized medicine.

Meningeal interleukin-17-producing T cells mediate cognitive impairment in a mouse model of salt-sensitive hypertension

Hypertension (HTN), a disease afflicting over one billion individuals worldwide, is a leading cause of cognitive impairment, the mechanisms of which remain poorly understood. In the present study, in a mouse model of HTN, we find that the neurovascular and cognitive dysfunction depends on interleukin (IL)-17, a cytokine elevated in individuals with HTN. However, neither circulating IL-17 nor brain angiotensin signaling can account for the dysfunction. Rather, IL-17 produced by T cells in the dura mater is the mediator released in the cerebrospinal fluid and activating IL-17 receptors on border-associated macrophages (BAMs). Accordingly, depleting BAMs, deleting IL-17 receptor A in brain macrophages or suppressing meningeal T cells rescues cognitive function without attenuating blood pressure elevation, circulating IL-17 or brain angiotensin signaling. Our data unveil a critical role of meningeal T cells and macrophage IL-17 signaling in the neurovascular and cognitive dysfunction in a mouse model of HTN.

Mechanisms and consequences of sex differences in immune responses

Biological sex differences refer to differences between males and females caused by the sex chromosome complement (that is, XY or XX), reproductive tissues (that is, the presence of testes or ovaries), and concentrations of sex steroids (that is, testosterone or oestrogens and progesterone). Although these sex differences are binary for most human individuals and mice, transgender individuals receiving hormone therapy, individuals with genetic syndromes (for example, Klinefelter and Turner syndromes) and people with disorders of sexual development reflect the diversity in sex-based biology. The broad distribution of sex steroid hormone receptors across diverse cell types and the differential expression of X-linked and autosomal genes means that sex is a biological variable that can affect the function of all physiological systems, including the immune system. Sex differences in immune cell function and immune responses to foreign and self antigens affect the development and outcome of diverse diseases and immune responses.

Deficiency of Complement C3a and C5a receptors Does Not Prevent Angiotensin II-Induced Hypertension and Hypertensive End-Organ Damage

BACKGROUND

Complement may drive the pathology of hypertension through effects on innate and adaptive immune responses. Recently an injurious role for the anaphylatoxin receptors C3aR (complement component 3a receptor) and C5aR1 (complement component 5a receptor) in the development of hypertension was shown through downregulation of Foxp3+ (forkhead box protein 3) regulatory T cells. Here, we deepen our understanding of the therapeutic potential of targeting both receptors in hypertension.

METHODS

Data from the European Renal cDNA Bank, single cell sequencing and immunohistochemistry were examined in hypertensive patients. The effect of C3aR or C3aR/C5aR1 double deficiency was assessed in two models of Ang II (angiotensin II)-induced hypertension in knockout mice.

RESULTS

We found increased expression of C3aR, C5aR1 and Foxp3 cells in kidney biopsies of patients with hypertensive nephropathy. Expression of both receptors was mainly found in myeloid cells. No differences in blood pressure, renal injury (albuminuria, glomerular filtration rate, glomerular and tubulointerstitial injury, inflammation) or cardiac injury (cardiac fibrosis, heart weight, gene expression) between control and mutant mice was discerned in C3aR-/- as well as C3aR/C5aR1-/- double knockout mice. The number of renal Tregs was not decreased in Ang II as well as in DOCA salt induced hypertension.

CONCLUSIONS

Hypertensive nephropathy in mice and men is characterized by an increase of renal regulatory T cells and enhanced expression of anaphylatoxin receptors. Our investigations do not corroborate a role for C3aR/C5aR1 axis in Ang II-induced hypertension hence challenging the concept of anaphylatoxin receptor targeting in the treatment of hypertensive disease.

Cardiometabolic Effects of DOCA-Salt in Mice Depend on Ambient Temperature

BACKGROUND

Mice prefer warmer environments than humans. For this reason, behavioral and physiological thermoregulatory responses are engaged by mice in response to a standard room temperature of 22 to 24 °C. Autonomic mechanisms mediating thermoregulatory responses overlap with mechanisms activated in hypertension, and, therefore, we hypothesized that housing at thermoneutral temperatures (TNs; 30 °C) would modify the cardiometabolic effects of deoxycorticosterone acetate (DOCA)-salt in mice.

METHODS

The effects of DOCA-salt treatment upon ingestive behaviors, energy expenditure, blood pressure, heart rate (HR), and core temperature were assessed in C57BL/6J mice housed at room temperature or TN.

RESULTS

Housing at TN reduced food intake, energy expenditure, blood pressure, and HR and attenuated HR responses to acute autonomic blockade by chlorisondamine. At room temperature, DOCA-salt caused expected increases in fluid intake, sodium retention in osmotically inactive pools, blood pressure, core temperature, and also caused expected decreases in fat-free mass, total body water, and HR. At TN, the effects of DOCA-salt upon fluid intake, fat gains, hydration, and core temperature were exaggerated, but effects on energy expenditure and HR were blunted. Effects of DOCA-salt upon blood pressure were similar for 3 weeks and exaggerated by TN housing in the fourth week.

CONCLUSIONS

Ambient temperature robustly influences behavioral and physiological functions in mice, including metabolic and cardiovascular phenotype development in response to DOCA-salt treatment. Studying cardiometabolic responses of mice at optimal ambient temperatures promises to improve the translational relevance of rodent models.

Genetic Ablation of Prorenin Receptor in the Rostral Ventrolateral Medulla Influences Blood Pressure and Hydromineral Balance in Deoxycorticosterone-Salt Hypertension

Non-enzymatic activation of renin via its interaction with prorenin receptor (PRR) has been proposed as a key mechanism of local renin-angiotensin system (RAS) activation. The presence of renin and angiotensinogen has been reported in the rostral ventrolateral medulla (RVLM). Overactivation of bulbospinal neurons in the RVLM is linked to hypertension (HTN). Previous studies have shown that the brain RAS plays a role in the pathogenesis of the deoxycorticosterone (DOCA)-salt HTN model. Thus, we hypothesized that PRR in the RVLM is involved in the local activation of the RAS, facilitating the development of DOCA-salt HTN. Selective PRR ablation targeting the RVLM (PRRRVLM-Null mice) resulted in an unexpected sex-dependent and biphasic phenotype in DOCA-salt HTN. That is, PRRRVLM-Null females (but not males) exhibited a significant delay in achieving maximal pressor responses during the initial stage of DOCA-salt HTN. Female PRRRVLM-Null subsequently showed exacerbated DOCA-salt-induced pressor responses during the "maintenance" phase with a maximal peak at 13 d on DOCA-salt. This exacerbated response was associated with an increased sympathetic drive to the resistance arterioles and the kidney, exacerbated fluid and sodium intake and output in response to DOCA-salt, and induced mobilization of fluids from the intracellular to extracellular space concomitant with elevated vasopressin. Ablation of PRR suppressed genes involved in RAS activation and catecholamine synthesis in the RVLM but also induced expression of genes involved in inflammatory responses. This study illustrates complex and sex-dependent roles of PRR in the neural control of BP and hydromineral balance through autonomic and neuroendocrine systems. Graphical abstract.

Endothelial mechanical stretch regulates the immunological synapse interface of renal endothelial cells in a sex-dependent manner

Increased mechanical endothelial cell stretch contributes to the development of numerous cardiovascular and renal pathologies. Recent studies have shone a light on the importance of sex-dependent inflammation in the pathogenesis of renal disease states. The endothelium plays an intimate and critical role in the orchestration of immune cell activation through upregulation of adhesion molecules and secretion of cytokines and chemokines. While endothelial cells are not recognized as professional antigen-presenting cells, in response to cytokine stimulation, endothelial cells can express both major histocompatibility complex (MHC) I and MHC II. MHCs are essential to forming a part of the immunological synapse interface during antigen presentation to adaptive immune cells. Whether MHC I and II are increased under increased mechanical stretch is unknown. Due to hypertension being multifactorial, we hypothesized that increased mechanical endothelial stretch promotes the regulation of MHCs and key costimulatory proteins on mouse renal endothelial cells (MRECs) in a stretch-dependent manner. MRECs derived from both sexes underwent 5%, 10%, or 15% uniaxial cyclical stretch, and immunological synapse interface proteins were determined by immunofluorescence microscopy, immunoblot analysis, and RNA sequencing. We found that increased endothelial mechanical stretch conditions promoted downregulation of MHC I in male MRECs but upregulation in female MRECs. Moreover, MHC II was upregulated by mechanical stretch in both male and female MRECs, whereas CD86 and CD70 were regulated in a sex-dependent manner. By bulk RNA sequencing, we found that increased mechanical endothelial cell stretch promoted differential gene expression of key antigen processing and presentation genes in female MRECs, demonstrating that females have upregulation of key antigen presentation pathways. Taken together, our data demonstrate that mechanical endothelial stretch regulates endothelial activation and immunological synapse interface formation in renal endothelial cells in a sex-dependent manner.NEW & NOTEWORTHY Endothelial cells contribute to the development of renal inflammation and have the unique ability to express antigen presentation proteins. Whether increased endothelial mechanical stretch regulates immunological synapse interface proteins remains unknown. We found that antigen presentation proteins and costimulatory proteins on renal endothelial cells are modulated by mechanical stretch in a sex-dependent manner. Our data provide novel insights into the sex-dependent ability of renal endothelial cells to present antigens in response to endothelial mechanical stimuli.

Cell-specific transcriptome changes in the hypothalamic arcuate nucleus in a mouse deoxycorticosterone acetate-salt model of hypertension

A common preclinical model of hypertension characterized by low circulating renin is the "deoxycorticosterone acetate (DOCA)-salt" model, which influences blood pressure and metabolism through mechanisms involving the angiotensin II type 1 receptor (AT1R) in the brain. More specifically, AT1R within Agouti-related peptide (AgRP) neurons of the arcuate nucleus of the hypothalamus (ARC) has been implicated in selected effects of DOCA-salt. In addition, microglia have been implicated in the cerebrovascular effects of DOCA-salt and angiotensin II. To characterize DOCA-salt effects upon the transcriptomes of individual cell types within the ARC, we used single-nucleus RNA sequencing (snRNAseq) to examine this region from male C57BL/6J mice that underwent sham or DOCA-salt treatment. Thirty-two unique primary cell type clusters were identified. Sub-clustering of neuropeptide-related clusters resulted in identification of three distinct AgRP subclusters. DOCA-salt treatment caused subtype-specific changes in gene expression patterns associated with AT1R and G protein signaling, neurotransmitter uptake, synapse functions, and hormone secretion. In addition, two primary cell type clusters were identified as resting versus activated microglia, and multiple distinct subtypes of activated microglia were suggested by sub-cluster analysis. While DOCA-salt had no overall effect on total microglial density within the ARC, DOCA-salt appeared to cause a redistribution of the relative abundance of activated microglia subtypes. These data provide novel insights into cell-specific molecular changes occurring within the ARC during DOCA-salt treatment, and prompt increased investigation of the physiological and pathophysiological significance of distinct subtypes of neuronal and glial cell types.

Signaling pathways in vascular function and hypertension: molecular mechanisms and therapeutic interventions

Hypertension is a global public health issue and the leading cause of premature death in humans. Despite more than a century of research, hypertension remains difficult to cure due to its complex mechanisms involving multiple interactive factors and our limited understanding of it. Hypertension is a condition that is named after its clinical features. Vascular function is a factor that affects blood pressure directly, and it is a main strategy for clinically controlling BP to regulate constriction/relaxation function of blood vessels. Vascular elasticity, caliber, and reactivity are all characteristic indicators reflecting vascular function. Blood vessels are composed of three distinct layers, out of which the endothelial cells in intima and the smooth muscle cells in media are the main performers of vascular function. The alterations in signaling pathways in these cells are the key molecular mechanisms underlying vascular dysfunction and hypertension development. In this manuscript, we will comprehensively review the signaling pathways involved in vascular function regulation and hypertension progression, including calcium pathway, NO-NOsGC-cGMP pathway, various vascular remodeling pathways and some important upstream pathways such as renin-angiotensin-aldosterone system, oxidative stress-related signaling pathway, immunity/inflammation pathway, etc. Meanwhile, we will also summarize the treatment methods of hypertension that targets vascular function regulation and discuss the possibility of these signaling pathways being applied to clinical work.

The link between immunity and hypertension in the kidney and heart

Hypertension is the primary cause of cardiovascular disease, which is a leading killer worldwide. Despite the prevalence of this non-communicable disease, still between 90% and 95% of cases are of unknown or multivariate cause ("essential hypertension"). Current therapeutic options focus primarily on lowering blood pressure through decreasing peripheral resistance or reducing fluid volume, but fewer than half of hypertensive patients can reach blood pressure control. Hence, identifying unknown mechanisms causing essential hypertension and designing new treatment accordingly are critically needed for improving public health. In recent years, the immune system has been increasingly implicated in contributing to a plethora of cardiovascular diseases. Many studies have demonstrated the critical role of the immune system in the pathogenesis of hypertension, particularly through pro-inflammatory mechanisms within the kidney and heart, which, eventually, drive a myriad of renal and cardiovascular diseases. However, the precise mechanisms and potential therapeutic targets remain largely unknown. Therefore, identifying which immune players are contributing to local inflammation and characterizing pro-inflammatory molecules and mechanisms involved will provide promising new therapeutic targets that could lower blood pressure and prevent progression from hypertension into renal or cardiac dysfunction.

Inflammation and oxidative stress in salt sensitive hypertension; The role of the NLRP3 inflammasome

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

Immune Cell Activation in Obesity and Cardiovascular Disease

PURPOSE OF REVIEW

In this review, we focus on immune cell activation in obesity and cardiovascular disease, highlighting specific immune cell microenvironments present in individuals with atherosclerosis, non-ischemic heart disease, hypertension, and infectious diseases.

RECENT FINDINGS

Obesity and cardiovascular disease are intimately linked and often characterized by inflammation and a cluster of metabolic complications. Compelling evidence from single-cell analysis suggests that obese adipose tissue is inflammatory and infiltrated by almost all immune cell populations. How this inflammatory tissue state contributes to more systemic conditions such as cardiovascular and infectious disease is less well understood. However, current research suggests that changes in the adipose tissue immune environment impact an individual's ability to combat illnesses such as influenza and SARS-CoV2. Obesity is becoming increasingly prevalent globally and is often associated with type 2 diabetes and heart disease. An increased inflammatory state is a major contributor to this association. Widespread chronic inflammation in these disease states is accompanied by an increase in both innate and adaptive immune cell activation. Acutely, these immune cell changes are beneficial as they sustain homeostasis as inflammation increases. However, persistent inflammation subsequently damages tissues and organs throughout the body. Future studies aimed at understanding the unique immune cell populations in each tissue compartment impacted by obesity may hold potential for therapeutic applications.

Sex Differences in the Immune System in Relation to Hypertension and Vascular Disease

Hypertension is the leading risk factor for cardiovascular disease and mortality worldwide. Despite intensive research into the mechanisms underlying the development of hypertension, it remains difficult to control blood pressure in a large proportion of patients. Young men have a higher prevalence of hypertension compared with age-matched women, and this holds true until approximately the fifth decade of life. Following the onset of menopause, the incidence of hypertension among women begins to surpass that of men. The immune system has been demonstrated to play a role in the pathophysiology of hypertension, and biological sex and sex hormones can affect the function of innate and adaptive immune cell populations. Recent studies in male and female animal models of hypertension have begun to unravel the relationship among sex, immunity, and hypertension. Hypertensive male animals show a bias toward proinflammatory T-cell subsets, including interleukin (IL) 17-producing T_H17 cells, and increased renal infiltration of T cells and inflammatory macrophages. Conversely, premenopausal female animals are largely protected from hypertension, and have a predilection for anti-inflammatory T regulatory cells and production of anti-inflammatory cytokines, such as IL-10. Menopause abrogates female protection from hypertension, which may be due to changes among anti-inflammatory T regulatory cell populations. Since development of novel treatments for hypertension has plateaued, determining the role of sex in the pathophysiology of hypertension may open new therapeutic avenues for both men and women.

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.

Implications of regulatory T cells in non-lymphoid tissue physiology and pathophysiology

Treg cells have been initially described as gatekeepers for the control of autoimmunity, as they can actively suppress the activity of other immune cells. However, their role goes beyond this as Treg cells further control immune responses during infections and tumor development. Furthermore, Treg cells can acquire additional properties for e.g., the control of tissue homeostasis. This is instructed by a specific differentiation program and the acquisition of effector properties unique to Treg cells in non-lymphoid tissues. These tissue Treg cells can further adapt to their tissue environment and acquire distinct functional properties through specific transcription factors activated by a combination of tissue derived factors, including tissue-specific antigens and cytokines. In this review, we will focus on recent findings extending our current understanding of the role and differentiation of these tissue Treg cells. As such we will highlight the importance of tissue Treg cells for tissue maintenance, regeneration, and repair in adipose tissue, muscle, CNS, liver, kidney, reproductive organs, and the lung.

Treatment of male and female spontaneously hypertensive rats with TNF-α inhibitor etanercept increases markers of renal injury independent of an effect on blood pressure

Hypertension remains the leading risk factor for cardiovascular disease. Young females tend to be protected from hypertension compared with age-matched males. Although it has become increasingly clear that the immune system plays a key role in the development of hypertension in both sexes, few studies have examined how cytokines mediate hypertension in males versus females. We previously published that there are sex differences in the levels of the cytokine tumor necrosis factor (TNF)-α in spontaneously hypertensive rats (SHR). The goal of this study was to test the hypothesis that TNF-α inhibition with etanercept will lower BP in male and female SHR. However, as male SHR have a more pro-inflammatory status than female SHR, we further hypothesize that males will have a greater decrease in BP with TNF-α inhibition than females. Young adult male and female SHR were administered increasing doses of the TNF-α inhibitor etanercept or vehicle twice weekly for 31 days and BP was continuously measured via telemetry. Following treatment, kidneys and urine were collected and analyzed for markers of inflammation and injury. Despite significantly decreasing renal TNF-α levels, renal phospho-NFκB and urinary MCP-1 excretion, etanercept did not alter BP in either male or female SHR. Interestingly, treatment with etanercept increased urinary excretion of protein, creatinine and KIM-1 in both sexes. These results indicate that TNF-α does not contribute to sex differences in BP in SHR but may be vital in the maintenance of renal health.

Sex Differences in TLR4 Expression in SHR Do Not Contribute to Sex Differences in Blood Pressure or the Renal T cell Profile

Hypertension is a primary risk factor for the development of cardiovascular disease. Mechanisms controlling blood pressure (BP) in men and women are still being investigated, however, there is increasing evidence supporting a role for the innate immune system. Specifically, Toll-like receptors (TLR), and TLR4 in particular, have been implicated in the development of hypertension in male spontaneously hypertensive rats (SHR). Despite established sex differences in BP control and inflammatory markers in hypertensive males and females, little is known regarding the role of TLR4 in hypertension in females. Our hypotheses were that male SHR have greater TLR4 expression compared to females, and that sex differences in TLR4 contribute to sex differences in BP and the T cell profile. To test these hypotheses, initial studies measured renal TLR4 protein expression in 13-week old male and female SHR. Additional SHR were implanted with telemetry devices and randomized to treatment with either IgG or TLR4 neutralizing antibodies. Untreated control male SHR have greater TLR4 protein expression in the kidney compared to females. However, treatment with TLR4 neutralizing antibody for 2 weeks did not significantly alter BP in either male or female SHR. Interestingly, neutralization of TLR4 increased renal CD3⁺ T cells in female SHR, with no alteration in CD4⁺ T cells or CD8⁺ T cells in either sex. Taken together, our data indicates that although male SHR have greater renal TLR4 expression than females, TLR4 does not contribute to the higher BP and more pro-inflammatory renal T cell prolife in males vs. females.

Pathophysiological Mechanisms of Hypertension Development Induced by Fructose Consumption

During the past several decades, there has been a dramatic increase in fructose consumption worldwide in parallel with epidemics of metabolic diseases. Accumulating evidence has suggested that excessive fructose consumption...

Interleukin-10 in the Vasculature: Pathophysiological Implications

Interleukin-10 (IL-10) is an important immunomodulatory cytokine, initially characterized as an anti-inflammatory agent released by immune cells during infectious and inflammatory processes. IL-10 exhibits biological functions that extend to the regulation of different intracellular signaling pathways directly associated with vascular function. This cytokine plays a vital role in vascular tone regulation through the change of important proteins involved in vasoconstriction and vasodilation. Numerous investigations covered here have shown that therapeutic strategies inducing IL-10 result in anti-inflammatory, anti-hypertrophic, antihyperplastic, anti-apoptotic and antihypertensive effects. This non-systematic review summarizes the modulating effects mediated by IL-10 in vascular tissue, particularly on vascular tone, and the intracellular pathway induced by this cytokine. We also highlight the advances in IL-10 manipulation as a therapeutic target in different cardiovascular pathophysiologies, including the physiological implications in animals and humans. Finally, the review illustrates current and potential future perspectives of the potential use of IL-10 in clinical trials, based on the clinical evidence.

Splenectomy increases blood pressure and abolishes sex differences in renal T-regulatory cells in spontaneously hypertensive rats

Over the past decade there has been increasing support for a role of the immune system in the development of hypertension. Our lab has previously reported that female spontaneously hypertensive rats (SHRs) have a blood pressure (BP)-dependent increase in anti-inflammatory renal regulatory T cells (Tregs), corresponding to lower BP compared with males. However, little is known regarding the mechanism for greater renal Tregs in females. The current study was designed to test the hypothesis that the greater relative abundance of renal Tregs in female SHR is due to greater Treg production. To test this hypothesis, T cell profiles were measured in the spleen by flow cytometry in male and female SHR at 5 and 14 weeks of age. Splenic Tregs did not differ between males and females, suggesting sex differences in renal Tregs is not due to differences in production. To assess the role of the spleen in sex differences in renal Tregs and BP control, rats were randomized to receive sham surgery (CON) or splenectomy (SPLNX) at 12 weeks of age and implanted with telemeters to measure BP. After 2 weeks, kidneys were harvested for flow cytometric analysis of T cells. Splenectomy increased BP in both sexes after 2 weeks. Renal Tregs decreased in both sexes after splenectomy, abolishing the sex differences in renal Tregs. In conclusion, splenic Tregs were comparable in male and female SHRs, suggesting that sex differences in renal Tregs is due to differences in renal Treg recruitment, not Treg production.

Sex differences in hypertension: lessons from spontaneously hypertensive rats (SHR)

Although numerous clinical and experimental studies have clearly identified a sexual dimorphism in blood pressure control, the mechanism(s) underlying gender differences in blood pressure remain unclear. Over the past two decades, numerous laboratories have utilized the spontaneously hypertensive rats (SHR) as an experimental model of essential hypertension to increase our understanding of the mechanisms regulating blood pressure in males and females. Previous work by our group and others have implicated that differential regulation of adrenergic receptors, the renin-angiotensin system, oxidative stress, nitric oxide bioavailability and immune cells contribute to sex differences in blood pressure control in SHR. The purpose of this review is to summarize previous findings to date regarding the mechanisms of blood pressure control in male versus female SHR.

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.

Aldosterone, Inflammation, Immune System, and Hypertension

Aldosterone is a mineralocorticoid hormone that controls body fluid and electrolyte balance. Excess aldosterone is associated with cardiovascular and metabolic diseases. Inflammation plays a critical role on vascular damage promoted by aldosterone and aggravates vascular abnormalities, including endothelial dysfunction, vascular remodeling, fibrosis and oxidative stress, and other manifestations of end-organ damage that are associated with hypertension, other forms of cardiovascular disease, and diabetes mellitus and the metabolic syndrome. Over the past few years, many studies have consistently shown that aldosterone activates cells of the innate and adaptive immune systems. Macrophages and T cells accumulate in the kidneys, heart, and vasculature in response to aldosterone, and infiltration of immune cells contributes to end-organ damage in cardiovascular and metabolic diseases. Aldosterone activates various subsets of innate immune cells such as dendritic cells and monocytes/macrophages, as well as adaptive immune cells such as T lymphocytes, and, by activation of mineralocorticoid receptors stimulates proinflammatory transcription factors and the production of adhesion molecules and inflammatory cytokines and chemokines. This review will briefly highlight some of the studies on the involvement of aldosterone in activation of innate and adaptive immune cells and its impact on the cardiovascular system. Since aldosterone plays a key role in many cardiovascular and metabolic diseases, these data will open up promising perspectives for the identification of novel biomarkers and therapeutic targets for prevention and treatment of diseases associated with increased levels of aldosterone, such as arterial hypertension, obesity, the metabolic syndrome, and heart failure.

The importance of bone marrow and the immune system in driving increases in blood pressure and sympathetic nerve activity in hypertension

NEW FINDINGS

What is the topic of this review? This manuscript provides a review of the current understanding of the role of the sympathetic nervous system in regulation of bone marrow-derived immune cells and the effect that the infiltrating bone marrow cells may have on perpetuation of the sympathetic over-activation in hypertension. What advances does it highlight? We highlight the recent advances in understanding of the neuroimmune interactions both peripherally and centrally as they relate to blood pressure control.

ABSTRACT

The sympathetic nervous system (SNS) plays a crucial role in maintaining physiological homeostasis, in part by regulating, integrating and orchestrating processes between many physiological systems, including the immune system. Sympathetic nerves innervate all primary and secondary immune organs, and all cells of the immune system express β-adrenoreceptors. In turn, immune cells can produce cytokines, chemokines and neurotransmitters capable of modulating neuronal activity and, ultimately, SNS activity. Thus, the essential role of the SNS in the regulation of innate and adaptive immune functions is mediated, in part, via β-adrenoreceptor-induced activation of bone marrow cells by noradrenaline. Interestingly, both central and systemic inflammation are well-established hallmarks of hypertension and its co-morbidities, including an inflammatory process involving the transmigration and infiltration of immune cells into tissues. We propose that physiological states that prolong β-adrenoreceptor activation in bone marrow can disrupt neuroimmune homeostasis and impair communication between the immune system and SNS, leading to immune dysregulation, which, in turn, is sustained via a central mechanism involving neuroinflammation.

Toll-Like Receptors Contribute to Sex Differences in Blood Pressure Regulation

Toll-like receptors (TLRs) play an important role in the innate immune system, and recently, they have been shown to be involved in the regulation of blood pressure. The incidence of hypertension is higher in men, and it increases in postmenopausal women. In fact, premenopausal women are protected from cardiovascular disease compared with age-matched men, and it is well established that this protective effect is lost with menopause. However, the molecular mechanisms underlying this protection in women are unknown. Whether or not it could be related to differential activation of the innate immune system remains to be elucidated. This review focuses on (1) the differences between men and women in TLR activation and (2) whether TLR activation may influence the regulation of blood pressure in a sex-dependent manner.

IL-10 treatment decreases blood pressure in male, but not female, spontaneously hypertensive rats

Interleukin-10 (IL-10) is an anti-inflammatory cytokine that induces nitric oxide (NO) production. IL-10 supplementation has been previously shown to lower blood pressure (BP) in male hypertensive mice, but the effect of exogenous IL-10 in hypertensive female rodents has not been studied. For the present study, we hypothesized that chronic infusion of IL-10 in hypertensive rats would lower BP concomitant with an increase in renal NO synthase (NOS) activity. Male and female spontaneously hypertensive rats (SHRs; 12 wk old) were randomized to receive IL-10 infusion by subcutaneous minipump (3.5 µg·kg^-1·day^-1) or serve as sham controls (n = 4-6 rats per treatment per sex). BP was measured by tail cuff before and after 2 wk of treatment. Renal T cells and IL-10 were measured by flow cytometry, and NOS activity was determined by conversion of radiolabeled arginine to radiolabeled citrulline. Female SHRs had greater IL-10⁺ renal cells than male SHRs and greater expression of the IL-10 receptor at baseline. BP did not change in female SHRs treated with IL-10, but BP significantly decreased following IL-10 infusion in male SHRs. Contrary to our hypothesis, NOS enzymatic activity decreased with IL-10 treatment in the renal inner medulla and cortex of both sexes. Renal regulatory T cells also decreased in both sexes after IL-10 treatment. In conclusion, despite male SHRs having less IL-10 and IL-10 receptor expression in the kidney compared with female SHRs, exogenous IL-10 selectively decreased BP only in male SHRs. Furthermore, our data suggest that exogenous IL-10-induced decreases in BP in male SHRs are not dependent on upregulating renal NOS activity.

Hypertensive female Sprague-Dawley rats require an intact nitric oxide synthase system for compensatory increases in renal regulatory T cells

We have previously shown that hypertensive female rats have more regulatory T cells (Tregs), which contribute more to blood pressure (BP) control in female versus male rats. Based on known protective properties of Tregs, the goal of the present study was to investigate the mechanisms by which female rats maintain Tregs. The present study was designed to 1) compare the impact of three hypertension models on the percentage of renal Tregs and 2) test the hypothesis that nitric oxide synthase (NOS) inhibition prevents increases in renal Tregs and exacerbates renal damage in female Sprague-Dawley rats. Rats (11-14 wk old) were randomized to one of the following four groups: control, norepinephrine (NE) infusion, angiotensin II infusion, or the NOS inhibitor N^ω-nitro-l-arginine methyl ester (l-NAME) in drinking water. BP was measured via tail cuff. After 2 wk of treatment, kidneys were isolated and processed to measure Tregs via flow cytometric analysis and renal injury via urinary albumin excretion, plasma creatinine, and histological analyses. Hypertensive treatments increased BP in all experimental animals. Increases in BP in norepinephrine-and angiotensin II-treated rats were associated with increases in renal Tregs versus control. In contrast, l-NAME treatment decreased Tregs compared with all groups. l-NAME treatment modestly increased albumin excretion. However, plasma creatinine was comparable among the groups, and there was no histological evidence of glomerular or tubular injury. This study provides insights into the mechanisms regulating renal Tregs and supports that an intact NOS system is crucial for female rats to have BP-related increases in renal Tregs.