Sex-specific T-cell regulation of angiotensin II-dependent hypertension

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.

Role of angiotensin converting enzyme in pathogenesis associated with immunity in cardiovascular diseases

Angiotensin converting enzyme (ACE) is not only a critical component in the renin-angiotensin system (RAS), but also suggested as an important mediator for immune response and activity, such as immune cell mobilization, metabolism, biogenesis of immunoregulatory molecules, etc. The chronic duration of cardiovascular diseases (CVD) has been increasingly considered to be triggered by uncontrolled pathologic immune reactions from myeloid cells and lymphocytes. Considering the potential anti-inflammatory effect of the traditional antihypertensive ACE inhibitor (ACEi), we attempt to elucidate whether ACE and its catalytically relevant substances as well as signaling pathways play a role in the immunity-related pathogenesis of common CVD, such as arterial hypertension, atherosclerosis and arrythmias. ACEi was also reported to benefit the prognoses of COVID-19-positive patients with CVD, and COVID-19 disease with preexisting CVD or subsequent cardiovascular damage is featured by a significant influx of immune cells and proinflammatory molecules, suggesting that ACE may also participate in COVID-19 induced cardiovascular injury, because COVID-19 disease basically triggers an overactive pathologic immune response. Hopefully, the ACE inhibition and manipulation of those associated bioactive signals could supplement the current medicinal management of various CVD and bring greater benefit to patients' cardiovascular health.

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.

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.

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.

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.

T-cells regulate albuminuria but not hypertension, renal histology, or the medullary transcriptome in the Dahl SSCD247+/+ rat

In the current study, we took advantage of the loss of protection from hypertension in SSCD247-/- rats to characterize the pathological effects of renal T-cells in isolation from the confounding effects of elevated renal perfusion pressure. Male SSCD247-/- and SSCD247+/+ littermates were fed 4.0% NaCl (high salt) diet to induce hypertension. Blood pressure was assessed continuously throughout the time course with radiotelemetry. Urine albumin and protein excretion were assessed on the final day of high salt. Renal injury and medullary transcriptome were assessed after completion of the high salt protocol. In contrast to previous studies, mean arterial pressure was not significantly different between SSCD247-/- and SSCD247+/+ rats. Despite this lack of pressure difference, urinary albumin was significantly lower in SSCD247-/- rats than their wild-type littermates. In the outer medulla, substantially more transcriptomic changes were found to correlate with endpoint blood pressure than with the absence of presence of renal T-cells. We also demonstrated that renal histological damage was driven by elevated renal perfusion pressure rather than the presence of renal T-cells. In conclusion, using the loss of protection from hypertension in SSCD247-/- rats, we demonstrated that renal perfusion pressure has more profound pathological effects on the kidney than renal T-cells. However, renal T-cells, independently of blood pressure, modulate the progression of albuminuria.NEW & NOTEWORTHY In vivo studies in a T-cell-deficient rat model of salt-sensitive hypertension (SSCD247-/- rats) were used to evaluate the role of T-cells on the development of hypertension and renal damage. Detailed physiological and transcriptomic analysis demonstrated no difference in blood pressure between rats with (SSCD247+/+) or without (SSCD247-/-) T-cells. Despite this, albuminuria was significantly lower in SSCD247-/- rats than SSCD247+/+ rats.

Functional NADPH oxidase 2 in T cells amplifies salt-sensitive hypertension and associated renal damage

Infiltrating T cells in the kidney amplify salt-sensitive (SS) hypertension and renal damage, but the mechanisms are not known. Genetic deletion of T cells (SSCD247-/-) or of the p67phox subunit of NADPH oxidase 2 (NOX2; SSp67phox-/-) attenuates SS hypertension in the Dahl SS rat. We hypothesized that reactive oxygen species produced by NOX2 in T cells drive the SS phenotype and renal damage. T cells were reconstituted by adoptively transferring splenocytes (∼10 million) from the Dahl SS (SS→CD247) rat, the SSp67phox-/- rat (p67phox→CD247), or only PBS (PBS→CD247) into the SSCD247-/- rat on postnatal day 5. Animals were instrumented with radiotelemeters and studied at 8 wk of age. There were no detectable differences in mean arterial pressure (MAP) or albuminuria between groups when rats were maintained on a low-salt (0.4% NaCl) diet. After 21 days of high-salt diet (4.0% NaCl), MAP and albuminuria were significantly greater in SS→CD247 rats compared with p67phox→CD247 and PBS→CD247 rats. Interestingly, there was no difference between p67phox→CD247 and PBS→CD247 rats in albuminuria or MAP after 21 days. The lack of CD3+ cells in PBS→CD247 rats and the presence of CD3+ cells in rats that received the T cell transfer demonstrated the effectiveness of the adoptive transfer. No differences in the number of CD3+, CD4+, or CD8+ cells were observed in the kidneys of SS→CD247 and p67phox→CD247 rats. These results indicate that reactive oxygen species produced by NOX2 in T cells participates in the amplification of SS hypertension and renal damage.NEW & NOTEWORTHY Our current work used the adoptive transfer of T cells that lack functional NADPH oxidase 2 into a genetically T cell-deficient Dahl salt-sensitive (SS) rat model. The results demonstrated that reactive oxygen species produced by NADPH oxidase 2 in T cells participate in the amplification of SS hypertension and associated renal damage and identifies a potential mechanism that exacerbates the salt-sensitive phenotype.

The role of dietary magnesium deficiency in inflammatory hypertension

Nearly 30% of adults consume less than the estimated average daily requirement of magnesium (Mg2+), and commonly used medications, such as diuretics, promote Mg2+ deficiency. Higher serum Mg2+ levels, increased dietary Mg2+ in-take, and Mg2+ supplementation are each associated with lower blood pressure, suggesting that Mg2+-deficiency contributes to the pathogenesis of hypertension. Antigen-presenting cells, such as monocytes and dendritic cells, are well-known to be involved in the pathogenesis of hypertension. In these cells, processes implicated as necessary for increased blood pressure include activation of the NLRP3 inflammasome, IL-1β production, and oxidative modification of fatty acids such as arachidonic acid, forming isolevuglandins (IsoLGs). We hypothesized that increased blood pressure in response to dietary Mg2+-depletion leads to increased NLRP3, IL-1β, and IsoLG production in antigen presenting cells. We found that a Mg2+-depleted diet (0.01% Mg2+ diet) increased blood pressure in mice compared to mice fed a 0.08% Mg2+ diet. Mg2+-depleted mice did not exhibit an increase in total body fluid, as measured by quantitative magnetic resonance. Plasma IL-1β concentrations were increased (0.13 ± 0.02 pg/mL vs. 0.04 ± 0.02 pg/mL). Using flow cytometry, we observed increased NLRP3 and IL-1β expression in antigen-presenting cells from spleen, kidney, and aorta. We also observed increased IsoLG production in antigen-presenting cells from these organs. Primary culture of CD11c+ dendritic cells confirmed that low extracellular Mg2+ exerts a direct effect on these cells, stimulating IL-1β and IL-18 production. The present findings show that NLRP3 inflammasome activation and IsoLG-adduct formation are stimulated when dietary Mg2+ is depleted. Interventions and increased dietary Mg2+ consumption may prove beneficial in decreasing the prevalence of hypertension and cardiovascular disease.

Sex-Specific Features of the Correlation between GWAS-Noticeable Polymorphisms and Hypertension in Europeans of Russia

The aim of the study was directed at studying the sex-specific features of the correlation between genome-wide association studies (GWAS)-noticeable polymorphisms and hypertension (HTN). In two groups of European subjects of Russia (n = 1405 in total), such as men (n = 821 in total: n = 564 HTN, n = 257 control) and women (n = 584 in total: n = 375 HTN, n = 209 control), the distribution of ten specially selected polymorphisms (they have confirmed associations of GWAS level with blood pressure (BP) parameters and/or HTN in Europeans) has been considered. The list of studied loci was as follows: (PLCE1) rs932764 A > G, (AC026703.1) rs1173771 G > A, (CERS5) rs7302981 G > A, (HFE) rs1799945 C > G, (OBFC1) rs4387287 C > A, (BAG6) rs805303 G > A, (RGL3) rs167479 T > G, (ARHGAP42) rs633185 C > G, (TBX2) rs8068318 T > C, and (ATP2B1) rs2681472 A > G. The contribution of individual loci and their inter-locus interactions to the HTN susceptibility with bioinformatic interpretation of associative links was evaluated separately in men's and women's cohorts. The men-women differences in involvement in the disease of the BP/HTN-associated GWAS SNPs were detected. Among women, the HTN risk has been associated with HFE rs1799945 C > G (genotype GG was risky; OR_GG = 11.15 p_permGG = 0.014) and inter-locus interactions of all 10 examined SNPs as part of 26 intergenic interactions models. In men, the polymorphism BAG6 rs805303 G > A (genotype AA was protective; OR_AA = 0.30 p_permAA = 0.0008) and inter-SNPs interactions of eight loci in only seven models have been founded as HTN-correlated. HTN-linked loci and strongly linked SNPs were characterized by pronounced polyvector functionality in both men and women, but at the same time, signaling pathways of HTN-linked genes/SNPs in women and men were similar and were represented mainly by immune mechanisms. As a result, the present study has demonstrated a more pronounced contribution of BP/HTN-associated GWAS SNPs to the HTN susceptibility (due to weightier intergenic interactions) in European women than in men.

Salt Sensitivity of Blood Pressure in Women

Several clinical and large population studies indicate that women are more salt-sensitive than men, yet the precise mechanisms by which the sexually dimorphic onset manifests remains incompletely understood. Here, we evaluate recent epidemiological data and highlight current knowledge from studies investigating sex-specific mechanisms of salt-sensitive blood pressure (SSBP). Emerging evidence indicates that women of all ethnicities are more salt-sensitive than men, at all ages both premenopausal and postmenopausal. However, menopause exacerbates severity and prevalence of SSBP, suggesting that female sex chromosomes predispose to and female sex hormones mitigate SSBP. Results from both human and rodent studies support the contribution of enhanced and inappropriate activation of the aldosterone-ECMR (endothelial cell mineralocorticoid receptor) axis promoting vascular dysfunction in females. Increases in adrenal response to angiotensin II, in association with higher ECMR expression and activation of endothelial ENaC (epithelial sodium channel) in females compared to males, are emerging as central players in the development of endothelial dysfunction and SSBP in females. Female sex increases the prevalence and susceptibility of SSBP and sex hormones and sex chromosome complement may exert antagonistic effects in the development of the female heightened SSBP.

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.

Hypertension in Women: The Current Understanding and Future Goals

Hypertension is one of the major contributing risk factor of cardiovascular diseases. Despite enormous advances in the preventive cardiology, hypertension remains the leading cause of death and disability in women. The article aims to focus on the gender specific differences in hypertension, and existing gaps in the current understanding of high blood pressure (BP) in women. Apart from epidemiological differences, hypertension in men and women has distinct pathophysiological mechanisms, impact on cardiovascular system, awareness and control. Prevalence of hypertension is higher in men than women till menopause; following this the prevalence rises steeply in women, and exceeds that of men above 75 years of age. Women with their estrogenic environment are relatively protected from high BP as their hormonal/chromosomal profile govern expression of alternate renin angiotensin axis (RAS) pathway and anti-inflammatory, vasodilatory, anti-proliferative immune cells whereas in males, classical RAS driven inflammatory, pro-hypertensive and proliferative milieu confers higher risk of hypertension. Thus, immunotherapy can have a potential therapeutic role in the treatment of hypertension in future. Cardiovascular consequences of high BP are worse in women than men in majority of trials. Women are now getting more aware of hypertension but the control of BP still remains poorer than men, especially in older age group. There are some noteworthy pharmacokinetic and pharmacogenomics gender differences in response to various antihypertensive drugs, which can be taken into consideration while choosing a particular class of drugs in female population. Standard treatment guidelines recommend same BP targets and management strategies in both the genders, but the trials so far have not been designed in a way to draw women specific conclusions on optimal cut-offs for diagnosis and treatment of BP due to under representation of women in majority of trials. More women centered analysis in future hypertension research projects can provide better scientific insights in various clinical aspects of hypertension.

Th17 cells-linked mechanisms mediate vascular dysfunction induced by testosterone in a mouse model of gender-affirming hormone therapy

Clinical data point to adverse cardiovascular events elicited by testosterone replacement therapy. Testosterone is the main hormone used in gender-affirming hormone therapy (GAHT) by transmasculine people. However, the cardiovascular impact of testosterone in experimental models of GAHT remains unknown. Sex hormones modulate T cells activation, and immune mechanisms contribute to cardiovascular risk. The present study evaluated whether testosterone negatively impacts female cardiovascular function by enhancing Th17 cells-linked effector mechanisms. Female (8 weeks-old) C57BL/6J mice received testosterone (48 mg.Kg^-1.week^-1) for 8 weeks. Male mice were used for phenotypical comparisons. The hormone-treatment in female mice increased circulating testosterone to levels observed in male mice. Testosterone increased lean body mass and body mass index, and decreased perigonadal fat mass, mimicking clinical findings. After 8 weeks, testosterone decreased endothelium-dependent vasodilation and increased circulating Th17 cells. After 24 weeks, testosterone increased blood pressure in female mice. Ovariectomy did not intensify phenotypical or cardiovascular effects by testosterone. Female mice lacking T and B cells [Rag1 knockout (^-/-)], as well as female mice lacking IL-17 receptor (IL-17Ra^-/-), did not exhibit vascular dysfunction induced by testosterone. Testosterone impaired endothelium-dependent vasodilation in female mice lacking γδ T cells, similarly to the observed in wild type female mice. Adoptive transfer of CD4⁺ T cells restored testosterone-induced vascular dysfunction in Rag1^-/- female mice. Together, these data suggest that CD4⁺ T cells, most likely Th17 cells, are central to vascular dysfunction induced by testosterone in female mice, indicating that changes in immune cells balance are important in the GAHT in transmasculine people.

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.

Angiotensin II and AT1a Receptors in the Proximal Tubules of the Kidney: New Roles in Blood Pressure Control and Hypertension

Contrary to public perception, hypertension remains one of the most important public health problems in the United States, affecting 46% of adults with increased risk for heart attack, stroke, and kidney diseases. The mechanisms underlying poorly controlled hypertension remain incompletely understood. Recent development in the Cre/LoxP approach to study gain or loss of function of a particular gene has significantly helped advance our new insights into the role of proximal tubule angiotensin II (Ang II) and its AT1 (AT1a) receptors in basal blood pressure control and the development of Ang II-induced hypertension. This novel approach has provided us and others with an important tool to generate novel mouse models with proximal tubule-specific loss (deletion) or gain of the function (overexpression). The objective of this invited review article is to review and discuss recent findings using novel genetically modifying proximal tubule-specific mouse models. These new studies have consistently demonstrated that deletion of AT1 (AT1a) receptors or its direct downstream target Na+/H+ exchanger 3 (NHE3) selectively in the proximal tubules of the kidney lowers basal blood pressure, increases the pressure-natriuresis response, and induces natriuretic responses, whereas overexpression of an intracellular Ang II fusion protein or AT1 (AT1a) receptors selectively in the proximal tubules increases proximal tubule Na+ reabsorption, impairs the pressure-natriuresis response, and elevates blood pressure. Furthermore, the development of Ang II-induced hypertension by systemic Ang II infusion or by proximal tubule-specific overexpression of an intracellular Ang II fusion protein was attenuated in mutant mice with proximal tubule-specific deletion of AT1 (AT1a) receptors or NHE3. Thus, these recent studies provide evidence for and new insights into the important roles of intratubular Ang II via AT1 (AT1a) receptors and NHE3 in the proximal tubules in maintaining basal blood pressure homeostasis and the development of Ang II-induced hypertension.

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.

Pre-Existing Hypertension Is Related with Disproportions in T-Lymphocytes in Older Age

Age-related immune deficiencies increase the risk of comorbidities and mortality. This study evaluated immunosenescence patterns by flow cytometry of naïve and memory T cell subpopulations and the immune risk profile (IRP), expressed as the CD4/CD8 ratio and IgG CMV related to comorbidities. The disproportions in naïve and memory T cells, as well as in the CD4/CD8 ratio, were analysed in 99 elderly individuals (71.9 ± 5.8 years) diagnosed with hypertension (n = 51) or without hypertension (n = 48), using an eight-parameter flow cytometer. The percentage of CD4+ T lymphocytes was significantly higher in hypertensive than other individuals independently from CMV infections, with approximately 34% having CD4/CD8 > 2.5, and only 4% of the elderly with hypertension having CD4/CD8 < 1. The elderly with a normal BMI demonstrated the CD4/CD8 ratio ≥ 1 or ≤ 2.5, while overweight and obese participants showed a tendency to an inverted CD4/CD8 ratio. CD4/CD8 ratio increased gradually with age and reached the highest values in participants aged >75 years. The decline in CD4+ naïve T lymphocytes was more prominent in IgG CMV+ men when compared to IgG CMV+ women. The changes in naïve and memory T lymphocyte population, CD4/CD8, and CMV seropositivity included in IRP are important markers of health status in the elderly that are dependent on hypertension.

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.

The role of the mineralocorticoid receptor in immune cells in in cardiovascular disease

Chronic low-grade inflammation and immune cell activation are important mechanisms in the pathophysiology of cardiovascular disease (CVD). Therefore, targeted immunosuppression is a promising novel therapy to lower cardiovascular risk. In this review, we identify the mineralocorticoid receptor (MR) on immune cells as a potential target to modulate inflammation. The MR is present in almost all cells of the cardiovascular system, including immune cells. Activation of the MR in innate and adaptive immune cells induces inflammation which can contribute to CVD, by inducing endothelial dysfunction and hypertension. Moreover, it accelerates atherosclerotic plaque formation and destabilization and impairs tissue regeneration after ischemic events. Identifying the molecular targets for these non-renal actions of the MR provide promising novel cardiovascular drug targets for mineralocorticoid receptor antagonists (MRAs), which are currently mainly applied in hypertension and heart failure.

T Cell Immunometabolism and Redox Signaling in Hypertension

PURPOSE OF REVIEW

In this article, we summarize the current literature supporting metabolic and redox signaling pathways as important mechanisms underlying T cell activation in the context of hypertension.

RECENT FINDINGS

T cell immunometabolism undergoes dramatic remodeling in order to meet the demands of T cell activation, differentiation, and proliferation. Recent evidence demonstrates that the T cell oxidation-reduction (redox) system also undergoes significant changes upon activation, which can itself modulate metabolic processes and T cell function. Dysregulation of these signaling pathways can lead to aberrant T cell activation and inappropriate ROS production, both of which are linked to pathological conditions like hypertension. While the contribution of T cells to the progression of hypertension has been thoroughly investigated, how T cell metabolism and redox signaling changes, both separately and together, is an area of study that remains largely untouched. This review presents evidence from our own laboratory as well as others to highlight the importance of these two mechanisms in the study of hypertension.

Chronic 3D Vascular-Immune Interface Established by Coculturing Pressurized Resistance Arteries and Immune Cells

[Figure: see text].

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.

Sex differences in angiotensin II-induced hypertension and kidney injury: role of AT1a receptors in the proximal tubule of the kidney

In the present study, we tested the hypothesis that there are significant sex differences in angiotensin II (Ang II)-induced hypertension and kidney injury using male and female wildtype (WT) and proximal tubule-specific AT1a receptor knockout mice (PT-Agtr1a-/-). Twelve groups (n=8-12 per group) of adult male and female WT and PT-Agtr1a-/- mice were infused with a pressor dose of Ang II via osmotic minipump for 2 weeks (1.5 mg/kg/day, i.p.) and simultaneously treated with or without losartan (20 mg/kg/day, p.o.) to determine the respective roles of AT1a receptors in the proximal tubules versus systemic tissues. Basal systolic, diastolic, and mean arterial pressure were approximately 13 ± 3 mmHg lower (P<0.01), while basal 24-h urinary Na+, K+, and Cl- excretion were significantly higher in both male and female PT-Agtr1a-/- mice than WT controls (P<0.01) without significant sex differences between different strains. Both male and female WT and PT-Agtr1a-/- mice developed hypertension (P<0.01), and the magnitudes of the pressor responses to Ang II were similar between male and female WT and PT-Agtr1a-/- mice (n.s.). Likewise, Ang II-induced hypertension was significantly attenuated in both male and female PT-Agtr1a-/- mice (P<0.01). Furthermore, losartan attenuated the hypertensive responses to Ang II to similar extents in both male and female WT and PT-Agtr1a-/- mice. Finally, Ang II-induced kidney injury was attenuated in PT-Agtr1a-/- mice (P<0.01). In conclusion, the present study demonstrates that deletion of AT1a receptors in the proximal tubules of the kidney attenuates Ang II-induced hypertension and kidney injury without revealing significant sex differences.

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.

Sex and the G Protein-Coupled Estrogen Receptor Impact Vascular Stiffness

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In Aged Females, the Enhanced Pressor Response to Angiotensin II Is Attenuated By Estrogen Replacement via an Angiotensin Type 2 Receptor-Mediated Mechanism

[Figure: see text].

Concentrations of vanadium in urine with hypertension prevalence and blood pressure levels

The associations of vanadium exposure with hypertension risk in animal studies are inconsistent. Furthermore, epidemiologic studies on this topic are scarce. We aimed to assess the associations of vanadium exposure with hypertension prevalence and blood pressure levels in a general Chinese population. We measured urinary vanadium concentrations in 1867 participants to evaluate their internal exposure levels. The associations of urinary vanadium concentrations, categorized into quartiles or treated as continuous variables by logarithm transformation (log2), with hypertension prevalence and blood pressure levels were assessed by the multivariable logistic and linear regression models, respectively. We used the restricted cubic spline model to evaluate the dose-response relationship. Compared with the bottom quartile of vanadium, participants in the third and fourth quartile had an adjusted odds ratio of 2.04 (95% CI:1.40, 2.96) and 2.08 (95% CI:1.42, 3.06) for hypertension, with a linear dose-response relationship. The corresponding number for a doubling of vanadium concentrations was 1.25 (95% CI:1.12, 1.39). Besides, a doubling of vanadium concentrations was associated with a 0.66 (95% CI: 0.01, 1.31) and 0.90 (95% CI: 0.50, 1.31) mm Hg increased systolic and diastolic blood pressure level, respectively. Vanadium exposure was associated with increased hypertension prevalence and blood pressure levels. Prospective studies are needed to confirm our findings in other populations.

Gender differences in the renal changes induced by a prolonged high-fat diet in rats with altered renal development

The mechanisms involved in renal dysfunction induced by high-fat diet (HFD) in subjects with altered renal development (ARDev) are understudied. The objective of this study is to examine whether there are sex-dependent differences in the mechanisms involved in the hypertension and deterioration of renal function in SD rats with prolonged HFD and ARDev. The role of angiotensin II (Ang II) in the arterial pressure (AP) increments, the renal hemodynamic sensitivity to Ang II, glomerular damage and changes in fat abdominal volume, plasma adipokine levels, renal NADPHp67phox expression, and renal infiltration of immune cells were examined. Hypertension and deterioration of renal function were enhanced (P < 0.05) in both sexes of rats with HFD and ARDev. The decrease (P < 0.05) of AP elicited by candesartan in hypertensive rats was similar to that induced by the simultaneous administration of candesartan and apocynin. The greater (P < 0.05) renal vasoconstriction induced by Ang II in both sexes of rats with HFD and ARDev was accompanied by an enhanced (P < 0.05) infiltration of CD-3 cells and macrophages in the renal cortex and renal medulla. The increments (P < 0.05) in the renal expression of NADPHp67phox and glomeruloesclerosis were greater (P < 0.05) in males than in females with HFD and ARDev. Our results suggest that the hypertension and deterioration of renal function induced by HFD in rats with ARDev are Ang II-dependent and mediated by increments in oxidative stress and immune system activation. Sex-dependent increments in oxidative stress and glomerular damage may contribute to the deterioration of renal function in these rats.

Sex hormone-like Effects of Icariin on T-cells immune modulation in spontaneously hypertensive rats

ETHNOPHARMACOLOGICAL RELEVANCE

Epimedium brevicornu Maxim as a Chinese herb, is recommended for the treatment of menopausal women with hypertension for 50 years. Icariin, as the main hydrophilic ingredient of Epimedium brevicornu Maxim, has been proven to be a plant sex hormone and lower blood pressure down. Here, we hypothesized that Icariin can regulate T cells differentiation which leads to the blood pressure decrease in castrated SHR rats.

AIM OF THE STUDY

The present study aimed to investigate the effects of the exogenous estrogen, androgen and Icariin on T-cell modulation in hypertension.

MATERIALS AND METHODS

Two weeks after castration, both male and female SHR rats were given estradiol, testosterone, and Icariin intervention respectively. Body weight, blood pressure, and heart rate were tested weekly. After six weeks, proportion of T helper cells (Th), cytotoxic T cells (Tc), and regulatory T cells (Tregs) in both peripheral blood mononuclear cells (PBMCs) and splenocytes were tested by flowcytometry. Serum levels of estrogen, testosterone, AngII, TNF-α, IL-17 were tested by Elisa. Aortic arches were isolated for HE and Masson staining. The expressions of ERβ and AR in aorta were tested by Western-blot.

RESULTS

In both male and female SHR rats, we found that Icariin and estradiol lower blood pressure, but testosterone elevates blood pressure. Similar as testosterone, Icariin can attenuate Tc and Th proportions and elevate Tregs proportion in both peripheral blood and splenocyte in male SHR, which can be blunt by flutamide. Besides, Icariin performs similar function as estradiol that attenuates Tc proportions and elevates Tregs proportion in both peripheral blood and splenocytes in female SHR, which leads to the lower blood pressure and can be partly blunt by fulvestrant. Testosterone increases AngII and TNF-α levels in serum, leading to the higher blood pressure in both male and female SHR rats.

CONCLUSION

These results verified that Icariin, as a plant sex hormone, can regulate T cells differentiation related to blood pressure decrease in SHR rats.

Polysaccharides of Sporoderm-Broken Spore of Ganoderma lucidum Modulate Adaptive Immune Function via Gut Microbiota Regulation

Ganoderma lucidum (Leyss.Fr.) Karst is one of the well-known medicinal macrofungi all over the world, and mounting researches have focused on the polysaccharides derived from the spores of G. lucidum. In the present study, BALB/c mice (n = 8-10) were administered with crude polysaccharides of G. lucidum spores (CPGS) and the refined polysaccharides of G. lucidum spores (RPGS) for 30 days to investigate their effect on the adaptive immune system. Results showed that CPGS and RPGS displayed diverse effects on the lymphocyte activity in the spleen. The splenocyte proliferation activity upon mitogen was suppressed by CPGS and RPGS, while the NK cell's tumor-killing ability was promoted by CPGS. Both CPGS and RPGS could increase the proportion of naïve T cells in thymus, but only RPGS significantly uplifted the percentage of T cells, as well as the T cell subsets, in peripheral blood, and promoted the activation by upregulating the expression of costimulatory factor CD28. Moreover, 16S sequencing results showed that the effects of CPGS and RPGS were closely related to the regulation of gut microbiota. β-diversity of the microbiome was evidently changed by CPGS and RPGS. The phytoestrogen/polysaccharide-metabolizing bacteria (Adlercreutzia, Parabacteroides, and Prevotella), and an unclassified Desulfovibrionaceae, were remarkably enriched by CPGS or RPGS, and functions involving carbohydrate metabolism, membrane transport, and lipid metabolism were regulated. Moreover, the enrichments of Adlercreutzia, Prevotella, and Desulfovibrionaceae were positively related to the immune regulation by CPGS and RPGS, while that of Parabacteroides displayed a negative correlation. These findings suggested a promising effect of the polysaccharide from sporoderm-broken spore of G. lucidum in immune regulation to promote health control.

Aldosterone-induced hypertension is sex-dependent, mediated by T cells and sensitive to GPER activation

AIMS

The G protein-coupled estrogen receptor 1 (GPER) may modulate some effects of aldosterone. In addition, G-1 (a GPER agonist) can lower blood pressure (BP) and promote T cell-mediated anti-inflammatory responses. This study aimed to test the effects of G-1 and G-15 (a GPER antagonist) on aldosterone-induced hypertension in mice and to examine the cellular mechanisms involved.

METHODS AND RESULTS

C57Bl/6 (wild-type, WT), RAG1-deficient and GPER-deficient mice were infused with vehicle, aldosterone (0.72 mg/kg/day S.C. plus 0.9% NaCl for drinking) ± G-1 (0.03 mg/kg/day S.C.) ± G-15 (0.3 mg/kg/day S.C.) for 14 days. G-1 attenuated aldosterone-induced hypertension in male WT but not male GPER-deficient mice. G-15 alone did not alter hypertension but it prevented the anti-hypertensive effect of G-1. In intact female WT mice, aldosterone-induced hypertension was markedly delayed and suppressed compared with responses in males, with BP remaining unchanged until after Day 7. In contrast, co-administration of aldosterone and G-15 fully increased BP within 7 days in WT females. Similarly, aldosterone robustly increased BP by Day 7 in ovariectomized WT females, and in both sexes of GPER-deficient mice. Whereas aldosterone had virtually no effect on BP in RAG1-deficient mice, adoptive transfer of T cells from male WT or male GPER-deficient mice into male RAG1-deficient mice restored the pressor response to aldosterone. This pressor effect could be attenuated by G-1 in RAG1-deficient mice that were reconstituted with either WT or GPER-deficient T cells, suggesting that G-1 does not act via T cells to lower BP.

CONCLUSION

Our findings indicate that although aldosterone-induced hypertension is largely mediated by T cells, it can be attenuated by activation of GPER on non-T cells, which accounts for the sex difference in sensitivity to the pressor effect.

The Challenge by Multiple Environmental and Biological Factors Induce Inflammation in Aging: Their Role in the Promotion of Chronic Disease

The aging process is driven by multiple mechanisms that lead to changes in energy production, oxidative stress, homeostatic dysregulation and eventually to loss of functionality and increased disease susceptibility. Most aged individuals develop chronic low-grade inflammation, which is an important risk factor for morbidity, physical and cognitive impairment, frailty, and death. At any age, chronic inflammatory diseases are major causes of morbimortality, affecting up to 5-8% of the population of industrialized countries. Several environmental factors can play an important role for modifying the inflammatory state. Genetics accounts for only a small fraction of chronic-inflammatory diseases, whereas environmental factors appear to participate, either with a causative or a promotional role in 50% to 75% of patients. Several of those changes depend on epigenetic changes that will further modify the individual response to additional stimuli. The interaction between inflammation and the environment offers important insights on aging and health. These conditions, often depending on the individual's sex, appear to lead to decreased longevity and physical and cognitive decline. In addition to biological factors, the environment is also involved in the generation of psychological and social context leading to stress. Poor psychological environments and other sources of stress also result in increased inflammation. However, the mechanisms underlying the role of environmental and psychosocial factors and nutrition on the regulation of inflammation, and how the response elicited for those factors interact among them, are poorly understood. Whereas certain deleterious environmental factors result in the generation of oxidative stress driven by an increased production of reactive oxygen and nitrogen species, endoplasmic reticulum stress, and inflammation, other factors, including nutrition (polyunsaturated fatty acids) and behavioral factors (exercise) confer protection against inflammation, oxidative and endoplasmic reticulum stress, and thus ameliorate their deleterious effect. Here, we discuss processes and mechanisms of inflammation associated with environmental factors and behavior, their links to sex and gender, and their overall impact on aging.

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.

Aortic remodeling is modest and sex-independent in mice when hypertension is superimposed on aging

OBJECTIVES

Increased central artery stiffness associates with cardiovascular disease. Among other factors, hypertension and aging are strong contributors to central artery stiffening, yet it has been difficult to separate their effects. Herein, we study isolated and combined effects of hypertension and aging on central artery remodeling in multiple mouse models as a function of sex.

METHODS

We biomechanically phenotyped the aorta as a function of two different methods of inducing hypertension [infusion of angiotensin II (AngII) or combining a high salt diet with inhibition of endothelial-derived nitric oxide synthase using L-NAME] in male and female wild-type and fibulin-5 null mice, the latter of which models aspects of aortic aging.

RESULTS

Despite increasing blood pressure similarly, salt + L-NAME led to adaptive and maladaptive remodeling in the abdominal and thoracic aorta, respectively, whereas AngII caused luminal dilatation but little remodeling of the wall. Importantly, effects of aging were more dramatic than those resulting from induced hypertension and, consequently, superimposing hypertension on aging led to modest additional changes in luminal radius and wall thickness, though wall stress and stiffness increased mainly because of the elevated pressure.

CONCLUSION

Our results suggest that effects of hypertension on aortic remodeling are modest when superimposed on aging in mice, largely independent of sex. These findings are consistent with general observations in humans and in spontaneously hypertensive rats, though separated here for the first time in a rodent model characterized by a severe loss of elastic fiber integrity similar to that found in the aged human aorta.

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.

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

Hypertension is the most common risk factor for cardiovascular disease, causing over 18 million deaths a year. Although the mechanisms controlling blood pressure (BP) in either sex remain largely unknown, T cells play a critical role in the development of hypertension. Further evidence supports a role for the immune system in contributing to sex differences in hypertension. The goal of the current study was to first, determine the impact of sex on the renal T-cell profiles in DOCA-salt hypertensive males and females and second, test the hypothesis that greater numbers of T regulatory cells (Tregs) in females protect against DOCA-salt-induced increases in BP and kidney injury. Male rats displayed greater increases in BP than females following 3 weeks of DOCA-salt treatment, although increases in renal injury were comparable between the sexes. DOCA-salt treatment resulted in an increase in proinflammatory T cells in both sexes; however, females had more anti-inflammatory Tregs than males. Additional male and female DOCA-salt rats were treated with anti-CD25 to decrease Tregs. Decreasing Tregs significantly increased BP only in females, thereby abolishing the sex difference in the BP response to DOCA-salt. This data supports the hypothesis that Tregs protect against the development of hypertension and are particularly important for the control of BP in females.

Splenocyte transfer exacerbates salt-sensitive hypertension in rats

NEW FINDINGS

What is the central question of this study? Recruitment of immune cells to the kidney potentiates hypertensive pathology, but more refined methods are needed to assess these cells functionally. Adoptive transfer studies of immune cells have been limited in rat models and especially in the study of salt-sensitive hypertension. We tested the hypothesis that splenocyte transfer into T-cell-deficient rats is sufficient to exacerbate salt-sensitive hypertension. What is the main finding and its importance? We demonstrate that transfer of splenocytes into T-cell-deficient animals exacerbates salt-sensitive hypertension, and an enrichment in the CD4⁺ compartment specifically induces this phenomenon.

ABSTRACT

Increasing evidence of immune system activation during the progression of hypertension and renal injury has led to a need for new methods to study individual cell types. Transfer of immune cells serves as a powerful tool to isolate effects of specific subsets. Transfer studies in Rag1^-/- mice have demonstrated an important role of T-cell activation in hypertension, but this approach has yielded limited success in rat models. Using the T-cell-deficient Dahl salt-sensitive (SS) rat, SS^CD247-/- , we hypothesized that splenocyte transfer from SS wild-type animals into SS^CD247-/- animals would populate the T-cell compartment. The Dahl SS background provides a model for studying salt-sensitive hypertension; therefore, we also tested whether the dietary salt content of the donor would confer differential salt sensitivity in the recipient. To test this, donors were maintained on either a low-salt or a high-salt diet, and at postnatal day 5 the recipients received splenocyte transfer from one of these groups before a high-salt diet challenge. We showed that splenocyte transfer elevated blood pressures while rats were fed low salt and exacerbated the salt-sensitive increase in pressure when they were fed fed high salt. Furthermore, transfer of splenocytes conferred exacerbated renal damage. Lastly, we confirmed the presence of T cells in the circulation and in the spleen, and that infiltration of immune cells, including T cells, macrophages and B cells, into the kidney was elevated in those receiving the transfer. Interestingly, the source of the splenocytes, from donors fed either a low-salt or a high-salt diet, did not significantly affect these salt-sensitive phenotypes.

Sympathetic Enhancement of Memory T-Cell Homing and Hypertension Sensitization

RATIONALE

Effector memory T lymphocytes (TEM cells) exacerbate hypertension in response to repeated hypertensive stimuli. These cells reside in the bone marrow for prolonged periods and can be reactivated on reexposure to the hypertensive stimulus.

OBJECTIVE

Because hypertension is associated with increased sympathetic outflow to the bone marrow, we hypothesized that sympathetic nerves regulate accumulation and reactivation of bone marrow-residing hypertension-specific TEM cells.

METHODS AND RESULTS

Using unilateral superior cervical ganglionectomy in wild-type C57BL/6 mice, we showed that sympathetic nerves create a bone marrow environment that supports residence of hypertension-specific CD8+ T cells. These cells, defined by their proliferative response on coculture with dendritic cells from Ang (angiotensin) II-infused mice, were reduced in denervated compared with innervated bone of Ang II-infused mice. Adoptively transferred CD8+ T cells from Ang II-infused mice preferentially homed to innervated compared with denervated bone. In contrast, ovalbumin responsive T cells from OT-I mice did not exhibit this preferential homing. Increasing superior cervical ganglion activity by activating Gq-coupled designer receptor exclusively activated by designer drug augmented CD8+ TEM bone marrow accumulation. Adoptive transfer studies using mice lacking β2AR (β2 adrenergic receptors) indicate that β2AR in the bone marrow niche, rather than T-cell β2AR is critical for TEM cell homing. Inhibition of global sympathetic outflow using Gi-coupled DREADD (designer receptor exclusively activated by designer drug) injected into the rostral ventrolateral medulla or treatment with a β2AR antagonist reduced hypertension-specific CD8+ TEM cells in the bone marrow and reduced the hypertensive response to a subsequent response to low dose Ang II.

CONCLUSIONS

Sympathetic nerves contribute to the homing and survival of hypertension-specific TEM cells in the bone marrow after they are formed in hypertension. Inhibition of sympathetic nerve activity and β2AR blockade reduces these cells and prevents the blood pressure elevation and renal inflammation on reexposure to hypertension stimuli.

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.

B6.Rag1 Knockout Mice Generated at the Jackson Laboratory in 2009 Show a Robust Wild-Type Hypertensive Phenotype in Response to Ang II (Angiotensin II)

A key finding supporting a causal role of the immune system in the pathogenesis of hypertension is the observation that RAG1 knockout mice on a C57Bl/6J background (B6.Rag1^-/-), which lack functional B and T cells, develop a much milder hypertensive response to Ang II (angiotensin II) than control C57Bl/6J mice. Here, we report that we never observed any Ang II resistance of B6.Rag1^-/- mice purchased directly from the Jackson Laboratory as early as 2009. B6.Rag1^-/- mice displayed nearly identical blood pressure increases monitored via radiotelemetry and hypertensive end-organ damage in response to different doses of Ang II and different levels of salt intake (0.02%, 0.3%, and 3% NaCl diet). Similarly, restoration of T-cell immunity by adoptive cell transfer did not affect the blood pressure response to Ang II in B6.Rag1^-/- mice. Full development of the hypertension-resistant phenotype in B6.Rag1^-/- mice appears to depend on the action of yet unidentified nongenetic modifiers in addition to the absence of functional T cells.

DP1 Activation Reverses Age-Related Hypertension Via NEDD4L-Mediated T-Bet Degradation in T Cells

BACKGROUND

Blood pressure often rises with aging, but exact mechanisms are still not completely understood. With aging, the level of proinflammatory cytokines increases in T lymphocytes. Prostaglandin D₂, a proresolution mediator, suppresses Type 1 T helper (Th1) cytokines through D-prostanoid receptor 1 (DP1). In this study, we aimed to investigate the role of the prostaglandin D₂/DP1 axis in T cells on age-related hypertension.

METHODS

To clarify the physiological and pathophysiological roles of DP1 in T cells with aging, peripheral blood samples were collected from young and older male participants, and CD4⁺ T cells were sorted for gene expression, prostaglandin production, and Western blot assays. Mice blood pressure was quantified by invasive telemetric monitor.

RESULTS

The prostaglandin D₂/DP1 axis was downregulated in CD4⁺ T cells from older humans and aged mice. DP1 deletion in CD4⁺ T cells augmented age-related hypertension in aged male mice by enhancing Th1 cytokine secretion, vascular remodeling, CD4⁺ T cells infiltration, and superoxide production in vasculature and kidneys. Conversely, forced expression of exogenous DP1 in T cells retarded age-associated hypertension in mice by reducing Th1 cytokine secretion. Tumor necrosis factor α neutralization or interferon γ deletion ameliorated the age-related hypertension in DP1 deletion in CD4⁺ T cells mice. Mechanistically, DP1 inhibited Th1 activity via the PKA (protein kinase A)/p-Sp1 (phosphorylated specificity protein 1)/neural precursor cell expressed developmentally downregulated 4-like (NEDD4L) pathway-mediated T-box-expressed-in-T-cells (T-bet) ubiquitination. T-bet deletion or forced NEDD4L expression in CD4⁺ T cells attenuated age-related hypertension in CD4⁺ T cell-specific DP1-deficient mice. DP1 receptor activation by BW245C prevented age-associated blood pressure elevation and reduced vascular/renal superoxide production in male mice.

CONCLUSIONS

The prostaglandin D₂/DP1 axis suppresses age-related Th1 activation and subsequent hypertensive response in male mice through increase of NEDD4L-mediated T-bet degradation by ubiquitination. Therefore, the T cell DP1 receptor may be an attractive therapeutic target for age-related hypertension.

Augmenting Renal Lymphatic Density Prevents Angiotensin II-Induced Hypertension in Male and Female Mice

BACKGROUND

Renal inflammation and immune cell infiltration are characteristic of several forms of hypertension. Our laboratory has previously demonstrated that renal-inflammation-associated lymphangiogenesis occurs in salt-sensitive and nitric-oxide-inhibition-induced hypertension. Moreover, enhancing renal lymphatic density prevented the development of these two forms of hypertension. Here, we investigated the effects of angiotensin II-induced hypertension on renal lymphatic vessel density in male and female mice.

METHODS

Wild-type and genetically engineered male and female mice were infused with angiotensin II for 2 or 3 weeks. Isolated splenocytes and peritoneal macrophages from mice, and commercially available mouse lymphatic endothelial cells were used for in vitro studies.

RESULTS

Compared to vehicle controls, angiotensin II-infused male and female mice had significantly increased renal lymphatic vessel density in association with pro-inflammatory immune cells in the kidneys of these mice. Direct treatment of lymphatic endothelial cells with angiotensin II had no effect as they lack angiotensin II receptors; however, angiotensin II treatment of splenocytes and peritoneal macrophages induced secretion of the lymphangiogenic growth factor VEGF-C in vitro. Utilizing our genetic mouse model of inducible renal lymphangiogenesis, we demonstrated that greatly augmenting renal lymphatic density prior to angiotensin II infusion prevented the development of hypertension in male and female mice and this was associated with a reduction in renal CD11c+F4/80- monocytes.

CONCLUSION

Renal lymphatics play a significant role in renal immune cell trafficking and blood pressure regulation, and represent a novel avenue of therapy for hypertension.

Renal T cell infiltration occurs despite attenuation of development of hypertension with hydralazine in Envigo's female Dahl rat maintained on a low-Na+ diet

Many studies have suggested that renal T cell infiltration contributes to the pathogenesis of salt-sensitive hypertension. To investigate this mechanism further, we determined T cell profiles in the kidney and lymphoid tissues as a function of blood pressure in the female Envigo Dahl salt-sensitive (SS) rat maintained on low-Na+ (LS) diet. Mean arterial pressure and heart rate were measured by telemetry in SS rats from 1 mo old (juvenile) to 4 mo old. Normotensive salt-resistant (SR) rats were included as controls. Frequencies of T helper (CD4+) cells were greater in the kidney, lymph nodes, and spleen in 4-mo-old hypertensive SS rats compared with normotensive SR animals and SS juvenile rats, suggesting that renal T cell infiltration contributes to hypertension in the SS rat on a LS diet. At 1.5 mo, half of the SS rats were treated with vehicle (Veh), and the rest received hydralazine (HDZ; 25 mg·kg-1·day-1) for 11 wk. HDZ impeded the development of hypertension compared with Veh-treated control rats [mean arterial pressure: 157 ± 4 mmHg in the Veh-treated group (n = 6) vs. 133 ± 3 mmHg in the HDZ-treated group (n = 7), P < 0.001] without impacting T helper cell frequencies in the tissues, suggesting that HDZ can overcome mechanisms of hypertension driven by renal T cell infiltration under the LS diet. Renal frequencies of CD4+CD25+ and CD4+CD25+FoxP3+ regulatory T cells were significantly higher in 4-mo-old hypertensive rats compared with normotensive SR rats and SS juvenile rats, suggesting that these T cell subpopulations play a compensatory role in the development of hypertension. Greater understanding of these T cell populations could lead to new therapeutic targets for treating inflammatory diseases associated with hypertension.

Tipping the scales: Are females more at risk for obesity- and high-fat diet-induced hypertension and vascular dysfunction?

Obesity is a common metabolic disorder that has become a widespread epidemic in several countries. Sex and gender disparities in the prevalence of cardiovascular disease (CVD) have been well documented with premenopausal women having a lower incidence of CVD than age-matched men. However, women are more likely than men to suffer from obesity, which can predispose them to a greater risk of CVD. The mechanisms underlying high-fat diet (HFD)- or obesity-induced hypertension are not well defined, although immune system activation and inflammation have been implicated in several studies. Further, the sex of the subject can have a profound influence on the immune response to hypertensive stimuli. Therefore, the purpose of this review is to examine the effects of sex and gender on the role of the immune system in HFD-induced hypertension and vascular dysfunction. LINKED ARTICLES: This article is part of a themed section on The Importance of Sex Differences in Pharmacology Research. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.21/issuetoc.