Elevated Serum Level of Interleukin 17 in a Population With Prehypertension

Immune mechanisms in the pathophysiology of hypertension

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

Association of Interleukin-17 Inhibitors With Hypertension in Patients With Autoimmune Diseases: A Systematic Review and Meta-analysis on Randomized Controlled Trials

The influence of interleukin (IL)-17 inhibition on blood pressure in patients with autoimmune diseases remains inconclusive. Our objective is to examine the risk of hypertension in patients with autoimmune diseases undergoing IL-17 inhibition therapies through meta-analysis of randomized, placebo-controlled trials. We obtained integrated data from PubMed, Embase, and ClinicalTrials.gov. Incident hypertension rates were calculated, and hazard ratios with 95% confidence intervals were analyzed, along with statistics to assess heterogeneity. Sequential analysis ensured conclusion reliability. In 30 randomized controlled trials involving 9909 patients with diverse autoimmune diseases treated with anti-IL-17 agents, our meta-analysis revealed a significant increase in hypertension risk (risk ratio 1.69, 95% confidence interval 1.24–2.31, P = 0.001), robustly supported by trial sequential analysis. Among the 4 agents (secukinumab, ixekizumab, bimekizumab, and brodalumab), only secukinumab exhibited a notable association with hypertension. Patients with various primary autoimmune diseases, particularly those with psoriatic arthritis, had a higher likelihood of developing hypertension; in rheumatic arthritis patient cohorts, anti-IL-17 agents did not elevate hypertension risk. Prolonged treatment duration correlated with an increased hypertension risk. Stratifying by sex, studies with a female predominance demonstrated a higher risk ratio for hypertension compared with male-predominant studies. This highlights that anti-IL-17 treatment escalates hypertension risk, emphasizing the need for extra caution when managing patients with autoimmune diseases (Registered by PROSPERO, CRD42016053112).

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.

Angiotensin II-induced a steeper blood pressure elevation in IL-23 receptor-deficient mice: Role of interferon-γ-producing T cells

A subset of interleukin (IL)-17A-producing γδ T cells called γδT17 cells may contribute to progression of hypertension. γδT17 cell development is in part dependent upon IL-23 receptor (IL-23R) stimulation. We hypothesized that angiotensin (Ang) II-induced blood pressure (BP) elevation and vascular injury would be blunted in Il23r knock-in (Il23r^gfp/gfp) mice deficient in functional IL-23R. To test this hypothesis, we infused wild-type (WT) and Il23r^gfp/gfp mice with Ang II (490 ng/kg/min, SC) for 7 or 14 days. We recorded BP by telemetry, assessed vascular function and remodeling using pressurized myography, and profiled T cell populations and cytokine production by flow cytometry. An additional set of Il23r^gfp/gfp mice was infused with Ang II for 7 days and injected with interferon (IFN)-γ-neutralizing or control antibodies. Il23r^gfp/gfp mice had smaller and stiffer mesenteric arteries and were not protected against Ang II-induced BP elevation. BP was higher in Il23r^gfp/gfp mice than WT mice from day 3 until day 9 of Ang II infusion. Il23r^gfp/gfp mice had less γδT17 cells and more IFN-γ-producing γδ, CD4⁺, and CD8⁺ T cells than WT mice. Seven days of Ang II infusion led to increased IFN-γ-producing γδ, CD4⁺, and CD8⁺ T cells in Il23r^gfp/gfp mice, whereas only IFN-γ-producing γδ T cells were increased in WT mice. Blocking IFN-γ with a neutralizing antibody reduced the pressor response to 7 days of Ang II infusion in Il23r^gfp/gfp mice. Functional IL-23R deficiency was associated with increased IFN-γ-producing T cells and exaggerated initial development of Ang II-induced hypertension, which was in part mediated by IFN-γ.

Psoriasis and Cardiometabolic Diseases: Shared Genetic and Molecular Pathways

A convincing deal of evidence supports the fact that severe psoriasis is associated with cardiovascular diseases. However, the precise underlying mechanisms linking psoriasis and cardiovascular diseases are not well defined. Psoriasis shares common pathophysiologic mechanisms with atherosclerosis and cardiovascular (CV) risk factors. In particular, polymorphism in the IL-23R and IL-23 genes, as well as other genes involved in lipid and fatty-acid metabolism, renin-angiotensin system and endothelial function, have been described in patients with psoriasis and with cardiovascular risk factors. Moreover, systemic inflammation in patients with psoriasis, including elevated serum proinflammatory cytokines (e.g., TNF-α, IL-17, and IL-23) may contribute to an increased risk of atherosclerosis, hypertension, alteration of serum lipid composition, and insulin resistance. The nonlinear and intricate interplay among various factors, impacting the molecular pathways in different cell types, probably contributes to the development of psoriasis and cardiovascular disease (CVD). Future research should, therefore, aim to fully unravel shared and differential molecular pathways underpinning the association between psoriasis and CVD.

Mineralocorticoid receptor blockade with spironolactone has no direct effect on plasma IL-17A and injury markers in urine from kidney transplant patients

Kidney transplantation is associated with increased risk of cardiovascular morbidity. Interleukin-17A (IL-17A) mediates kidney injury. Aldosterone promotes T-helper-17 (Th-17) lymphocyte differentiation and IL-17A production through the mineralocorticoid receptor (MR). In this exploratory, post-hoc substudy, it was hypothesized that 1-year intervention with the MR antagonist spironolactone lowers IL-17A and related cytokines and reduces epithelial injury in kidney transplant recipients. Plasma and urine samples were obtained from kidney transplant recipients from a double-blind randomized clinical trial testing spironolactone (n=39) versus placebo (n=41). Plasma concentrations of cytokines IFN-γ, IL-17A, TNF-α, IL-6, IL-1β, and IL-10 were determined before and after 1-year treatment. Urine calbindin, clusterin, KIM-1, osteoactivin, TFF3, and VEGF/creatinine ratios were analyzed. Blood pressure and plasma aldosterone concentration at inclusion did not relate to plasma cytokines and injury markers. None of the cytokines changed in plasma after spironolactone intervention. Plasma IL-17A increased in the placebo group. Spironolactone induced an increase in plasma K⁺ (0.4 ± 0.4 mmol/L). This increase did not correlate with plasma IL-17A or urine calbindin and TFF3 changes. Ongoing treatment at inclusion with angiotensin-converting-enzyme inhibitor and/or angiotensin II receptor blockers was not associated with changed levels of IL-17A and injury markers and had no effect on the response to spironolactone. Urinary calbindin and TFF3 decreased in the spironolactone group with no difference in between-group analyses. In conclusion, irrespective of ongoing ANGII inhibition, spironolactone has no effect on plasma IL-17A and related cytokines or urinary injury markers in kidney transplant recipients.

Interleukin-17A: Potential mediator and therapeutic target in hypertension

Interleukin-17A (IL-17A) is a proinflammatory cytokine produced by cells of the immune system, predominantly Th17 and γδ lymphocytes. In this paper, we review the role of IL-17A in the pathogenesis of hypertension and in target organ damage. Preclinical studies in mice have shown that systemic adminstration of IL-17A increases blood pressure, probably by acting on multiple levels. Furthermore, IL-17A plasma concentrations are already elevated in patients with mild or moderate hypertension. Many studies in hypertensive mice models have detected IL-17A-producing cells in target organs such as the heart, vessels and kidneys. Patients with hypertensive nephrosclerosis show kidney infiltration by Th17 lymphocytes and γδ lymphocytes that express IL-17A. In addition, in experimental models of hypertension, the blockade of IL-17A by genetic strategies or using neutralizing antibodies, disminished blood pressure, probablyby acting on the small mesenteric arteries as well as in the regulation of tubule sodium transport. Moreover, IL-17A inhibition reduces end-organs damage. As a whole, the data presented in this review suggest that IL-17A participates in the regulation of blood pressure and in the genesis and maintenance of arterial hypertension, and may constitute a therapeutic target of hypertension-related pathologies in the future.

[Interleukin-17A: Possible mediator and therapeutic target in hypertension]

Interleukin-17A (IL-17A) is a proinflammatory cytokine produced by cells of the immune system, predominantly Th17 lymphocytes and γδ lymphocytes. In this paper, we review the role of IL-17A in the pathogenesis of hypertension and target organ damage. Studies in mice have shown that IL-17A increases blood pressure, probably by acting on multiple levels. Furthermore, IL-17A plasma concentrations are already elevated in patients with mild or moderate hypertension. Preclinical studies on arterial hypertension have detected IL-17A-producing cells in target organs such as the heart, vessels and kidneys. Patients with hypertensive nephrosclerosis show kidney infiltration by Th17 lymphocytes and γδ lymphocytes that express IL-17A. In addition, in experimental models of hypertension, blocking IL-17A by genetic strategies, or using neutralising antibodies, lowers blood pressure by acting on the vascular wall and tubule sodium transport and reduces damage to target organs. As a whole, the data presented in this review suggest that IL-17A participates in the regulation of blood pressure and in the genesis and maintenance of arterial hypertension, and may constitute a therapeutic target in the future.

T helper 17 cells in the pathophysiology of acute and chronic kidney disease

Both acute and chronic kidney disease have a strong underlying inflammatory component. This review focuses primarily on T helper 17 (Th17) cells as mediators of inflammation and their potential to modulate acute and chronic kidney disease. We provide updated information on factors and signaling pathways that promote Th17 cell differentiation with specific reference to kidney disease. We highlight numerous clinical studies that have investigated Th17 cells in the setting of human kidney disease and provide updated summaries from various experimental animal models of kidney disease indicating an important role for Th17 cells in renal fibrosis and hypertension. We focus on the pleiotropic effects of Th17 cells in different renal cell types as potentially relevant to the pathogenesis of kidney disease. Finally, we highlight studies that present contrasting roles for Th17 cells in kidney disease progression.

Interleukin 17A: Key Player in the Pathogenesis of Hypertension and a Potential Therapeutic Target

PURPOSE OF REVIEW

To summarize key advances in our understanding of the role of interleukin 17A (IL-17A) in the pathogenesis of hypertension and highlight important areas for future research and clinical translation.

RECENT FINDINGS

While T helper 17 (Th17) cells are major producers of IL-17A, there are several additional innate and adaptive immune cell sources including gamma-delta T cells, innate lymphoid cells, and natural killer cells. IL-17A promotes an increase in blood pressure through multiple mechanisms including inhibiting endothelial nitric oxide production, increasing reactive oxygen species formation, promoting vascular fibrosis, and enhancing renal sodium retention and glomerular injury. IL-17A production from Th17 cells is increased by high salt conditions in vitro and in vivo. There is also emerging data linking salt, the gut microbiome, and intestinal T cell IL-17A production. Novel therapeutics targeting IL-17A signaling are approved for the treatment of autoimmune diseases and show promise in both animal models of hypertension and human studies. Hypertensive stimuli enhance IL-17A production. IL-17A is a key mediator of renal and vascular dysfunction in hypertensive mouse models and correlates with hypertension in humans. Large randomized clinical trials are needed to determine whether targeting IL-17A might be an effective adjunct treatment for hypertension and its associated end-organ dysfunction.

Contribution of Th17 cells to tissue injury in hypertension

PURPOSE OF REVIEW

Hypertension has been demonstrated to be a chief contributor to morbidity and mortality throughout the world. Although the cause of hypertension is multifactorial, emerging evidence, obtained in experimental studies, as well as observational studies in humans, points to the role of inflammation and immunity. Many aspects of immune function have now been implicated in hypertension and end-organ injury; this review will focus upon the recently-described role of Th17 cells in this pathophysiological response.

RECENT FINDINGS

Studies in animal models and human genetic studies point to a role in the adaptive immune system as playing a contributory role in hypertension and renal tissue damage. Th17 cells, which produce the cytokine IL17, are strongly pro-inflammatory cells, which may contribute to tissue damage if expressed in chronic disease conditions. The activity of these cells may be enhanced by physiological factors associated with hypertension such as dietary salt or Ang II. This activity may culminate in the increased sodium retaining activity and exacerbation of inflammation and renal fibrosis via multiple cellular mechanisms.

SUMMARY

Th17 cells are a distinct component of the adaptive immune system that may strongly enhance pathways leading to increased sodium reabsorption, elevated vascular tone and end-organ damage. Moreover, this pathway may lend itself towards specific targeting for treatment of kidney disease and hypertension.

A narrative review of prehypertension and the cardiovascular system: effects and potential pathogenic mechanisms

In 1939, Robinson and Brucer first proposed the concept of prehypertension (PHTN), which was defined as a systolic blood pressure of 120–139 mmHg and/or diastolic blood pressure of 80–89 mmHg. PHTN is a major global health risk that adversely affects human health, especially the cardiovascular system. People with PHTN have a higher risk of developing cardiovascular diseases, including stroke, coronary heart disease, myocardial infarction and total cardiovascular events. However, there are few systematic summaries of the relationship between PHTN and the cardiovascular system. Furthermore, because the definition of ‘normal BP’ and the advantages of more intensive BP control remain unclear, there is no consensus on optimal interventions. In an attempt to provide information for clinicians or professionals who are interested in reducing the risk associated with PHTN, we review the existing studies to provide references for them with the effects of PHTN on the cardiovascular system and the potential pathogenic mechanisms of PHTN, including inflammatory responses, insulin resistance, endothelial dysfunction, sympathovagal imbalance, activation of the renin-angiotensin system and others. PHTN is highly prevalent and has adverse effects on health. An effective public health strategy is important to prevent the progression of PHTN. We envisage that this information will increase the public attention of PHTN and help to provide more strategies to reduce the risk of cardiovascular events.

IL-17A as a Potential Therapeutic Target for Patients on Peritoneal Dialysis

Chronic kidney disease (CKD) is a health problem reaching epidemic proportions. There is no cure for CKD, and patients may progress to end-stage renal disease (ESRD). Peritoneal dialysis (PD) is a current replacement therapy option for ESRD patients until renal transplantation can be achieved. One important problem in long-term PD patients is peritoneal membrane failure. The mechanisms involved in peritoneal damage include activation of the inflammatory and immune responses, associated with submesothelial immune infiltrates, angiogenesis, loss of the mesothelial layer due to cell death and mesothelial to mesenchymal transition, and collagen accumulation in the submesothelial compact zone. These processes lead to fibrosis and loss of peritoneal membrane function. Peritoneal inflammation and membrane failure are strongly associated with additional problems in PD patients, mainly with a very high risk of cardiovascular disease. Among the inflammatory mediators involved in peritoneal damage, cytokine IL-17A has recently been proposed as a potential therapeutic target for chronic inflammatory diseases, including CKD. Although IL-17A is the hallmark cytokine of Th17 immune cells, many other cells can also produce or secrete IL-17A. In the peritoneum of PD patients, IL-17A-secreting cells comprise Th17 cells, γδ T cells, mast cells, and neutrophils. Experimental studies demonstrated that IL-17A blockade ameliorated peritoneal damage caused by exposure to PD fluids. This article provides a comprehensive review of recent advances on the role of IL-17A in peritoneal membrane injury during PD and other PD-associated complications.

Role of interleukin-23/interleukin-17 axis in T-cell-mediated actions in hypertension

Current knowledge suggests that hypertension is in part mediated by immune mechanisms. Both interleukin (IL)-23 and IL-17 are up-regulated in several experimental hypertensive rodent models, as well as in hypertensive humans in observational studies. Recent preclinical studies have shown that either IL-23 or IL-17A treatment induce blood pressure elevation. However, the IL-23/IL-17 axis has not been a major therapeutic target in hypertension, unlike in other autoimmune diseases. In this review, we summarize current knowledge on the role of these cytokines in immune mechanisms contributing to hypertension, and discuss the potential of IL-23/IL-17-targeted therapy for treatment of hypertension.

Interleukin-17A induces vascular remodeling of small arteries and blood pressure elevation

An important link exists between hypertension and inflammation. Hypertensive patients present elevated circulating levels of proinflammatory cytokines, including interleukin-17A (IL-17A). This cytokine participates in host defense, autoimmune and chronic inflammatory pathologies, and cardiovascular diseases, mainly through the regulation of proinflammatory factors. Emerging evidence also suggests that IL-17A could play a role in regulating blood pressure and end-organ damage. Here, our preclinical studies in a murine model of systemic IL-17A administration showed that increased levels of circulating IL-17A raised blood pressure induced inward remodeling of small mesenteric arteries (SMAs) and arterial stiffness. In IL-17A-infused mice, treatment with hydralazine and hydrochlorothiazide diminished blood pressure elevation, without modifying mechanical and structural properties of SMA, suggesting a direct vascular effect of IL-17A. The mechanisms of IL-17A seem to involve an induction of vascular smooth muscle cell (VSMC) hypertrophy and phenotype changes, in the absence of extracellular matrix (ECM) proteins accumulation. Accordingly, treatment with an IL-17A neutralizing antibody diminished SMA remodeling in a model of angiotensin II (Ang II) infusion. Moreover, in vitro studies in VSMCs reported here, provide further evidence of the direct effects of IL-17A on cell growth responses. Our experimental data suggest that IL-17A is a key mediator of vascular remodeling of the small arteries, which might contribute, at least in part, to blood pressure elevation.

Associations between honey consumption and prehypertension in adults aged 40 years and older

Background: Honey has been shown to have multiple positive effects on human health. However, data on the associations of honey consumption with prehypertension are scarce. The aim of this study was to investigate whether honey consumption is associated with prehypertension in a Chinese population. Method: A cross-sectional study was conducted in 4,561 individuals aged ≥40 years. A validated 100-item semi-quantitative food frequency questionnaire was used to assess honey consumption. Blood pressure was measured at least twice by trained nurses. Multiple logistic regression models were used to explore the associations between honey consumption and prehypertension. Results: After adjustment for potential confounders, the odds ratios and 95% confidence intervals of prehypertension across increasing frequency of honey consumption were 1.00 (reference) for almost never, 1.17 (0.96, 1.41) for ≤6 times/week, and 1.25 (0.86, 1.84) for ≥7 times/week in men (P _{for trend} = 0.09); 1.00 (reference) for almost never, 0.76 (0.62, 0.92) for ≤6 times/week, and 0.84 (0.63, 1.12) for ≥7 times/week in women (P _{for trend} = 0.055), respectively. Conclusion: Our results showed that light-to-moderate intake of honey was associated with lower prevalence of prehypertension in women, but not men. Future studies are required to confirm these associations.

Pathogenic Pathways and Therapeutic Approaches Targeting Inflammation in Diabetic Nephropathy

Diabetic nephropathy (DN) is associated with an increased morbidity and mortality, resulting in elevated cost for public health systems. DN is the main cause of chronic kidney disease (CKD) and its incidence increases the number of patients that develop the end-stage renal disease (ESRD). There are growing epidemiological and preclinical evidence about the close relationship between inflammatory response and the occurrence and progression of DN. Several anti-inflammatory strategies targeting specific inflammatory mediators (cell adhesion molecules, chemokines and cytokines) and intracellular signaling pathways have shown beneficial effects in experimental models of DN, decreasing proteinuria and renal lesions. A number of inflammatory molecules have been shown useful to identify diabetic patients at high risk of developing renal complications. In this review, we focus on the key role of inflammation in the genesis and progression of DN, with a special interest in effector molecules and activated intracellular pathways leading to renal damage, as well as a comprehensive update of new therapeutic strategies targeting inflammation to prevent and/or retard renal injury.

Interleukin-17 signaling mediates cytolytic natural killer cell activation in response to placental ischemia

T-helper (T_H)17s, IL-17, and cytolytic natural killer cells (cNKs) are increased in preeclampsia and contribute to the hypertension, inflammation, and fetal growth restriction that occurs in response to placental ischemia in the reduced uterine perfusion pressure (RUPP) rat model of preeclampsia. As IL-17 stimulates NK cytotoxicity in vitro, we tested the hypothesis that IL-17 inhibition in RUPP rats would decrease cNK activation as a mechanism to improve maternal and fetal outcomes. On gestation day (GD) 14, rats undergoing RUPP received a miniosmotic pump infusing IL-17RC (100 pg/day), a soluble IL-17 receptor (RUPP + IL-17RC). On GD19, mean arterial pressure (MAP) was measured in normal pregnant (NP), RUPP, and RUPP + IL-17RC rats (n = 10-12/group), animals were euthanized, and blood and tissues were collected for analysis. MAP was 30% higher in RUPP compared with NP (P < 0.0001) and was 12% lower in RUPP + IL-17RC (P = 0.0007 vs. RUPP). Placental cytolytic NK cells were 132% higher in RUPP than in NP (P = 0.04 vs. NP) and were normalized in RUPP + IL-17RC (P = 0.03 vs. RUPP). Placental levels of TNF-α, a cNK-secreted cytokine, and macrophage inflammatory protein-3α (MIP-3α), a cNK chemokine, were higher in RUPP vs. NP and lower after IL-17 blockade. Placental VEGF was lower in RUPP vs. NP and was normalized in RUPP + IL-17RC. In vitro cytolytic activity of RUPP placental NKs was higher compared with NP and was blunted in RUPP + IL-17RC NKs. Finally, both fetal weight and placental weight were lower in RUPP compared with NP, and were improved in RUPP + IL-17RC. These data identify IL-17 as a mediator of cNK activation in response to placental ischemia during pregnancy.

Could IL-17A Be a Novel Therapeutic Target in Diabetic Nephropathy?

Chronic kidney disease has become a major medical issue in recent years due to its high prevalence worldwide, its association with premature mortality, and its social and economic implications. A number of patients gradually progress to end-stage renal disease (ESRD), requiring then dialysis and kidney transplantation. Currently, approximately 40% of patients with diabetes develop kidney disease, making it the most prevalent cause of ESRD. Thus, more effective therapies for diabetic nephropathy are needed. In preclinical studies of diabetes, anti-inflammatory therapeutic strategies have been used to protect the kidneys. Recent evidence supports that immune cells play an active role in the pathogenesis of diabetic nephropathy. Th17 immune cells and their effector cytokine IL-17A have recently emerged as promising targets in several clinical conditions, including renal diseases. Here, we review current knowledge regarding the involvement of Th17/IL-17A in the genesis of diabetic renal injury, as well as the rationale behind targeting IL-17A as an additional therapy in patients with diabetic nephropathy.

Interleukin 17A Participates in Renal Inflammation Associated to Experimental and Human Hypertension

Hypertension is now considered as an inflammatory disease, and the kidney is a key end-organ target. Experimental and clinical studies suggest that interleukin 17A (IL-17A) is a promising therapeutic target in immune and chronic inflammatory diseases, including hypertension and kidney disease. Elevated circulating IL-17A levels have been observed in hypertensive patients. Our aim was to investigate whether chronically elevated circulating IL-17A levels could contribute to kidney damage, using a murine model of systemic IL-17A administration. Blood pressure increased after 14 days of IL-17A infusion in mice when compared with that in control mice, and this was associated to kidney infiltration by inflammatory cells, including CD3⁺ and CD4⁺ lymphocytes and neutrophils. Moreover, proinflammatory factors and inflammatory-related intracellular mechanisms were upregulated in kidneys from IL-17A-infused mice. In line with these findings, in the model of angiotensin II infusion in mice, IL-17A blockade, using an anti-IL17A neutralizing antibody, reduced kidney inflammatory cell infiltrates and chemokine overexpression. In kidney biopsies from patients with hypertensive nephrosclerosis, IL-17A positive cells, mainly Th17 and γδ T lymphocytes, were found. Overall, the results support a pathogenic role of IL-17A in hypertensive kidney disease-associated inflammation. Therapeutic approaches targeting this cytokine should be explored to prevent hypertension-induced kidney injury.

Adaptive Immunity in Hypertension

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

Tissue Transglutaminase-Mediated AT1 Receptor Sensitization Underlies Pro-inflammatory Cytokine LIGHT-Induced Hypertension

BACKGROUND

Although numerous recent studies have shown a strong link between inflammation and hypertension, the underlying mechanisms by which inflammatory cytokines induce hypertension remain to be fully elucidated. Hypertensive disorders are also associated with elevated pressor sensitivity. Tissue transglutaminase (TG2), a potent cross-linking enzyme, is known to be transcriptionally activated by inflammatory cytokines and stabilize angiotensin II (Ang II) receptor AT₁ (AT₁R) via ubiquitination-preventing posttranslational modification. Here we sought to investigate the TG2-mediated AT₁R stabilization in inflammation-induced hypertension and its functional consequences with a focus on receptor abundance and Ang II responsiveness.

METHODS AND RESULTS

Using an experimental model of inflammation-induced hypertension established by introducing the pro-inflammatory tumor necrosis factor cytokine LIGHT, we provide pharmacologic and genetic evidence that TG2 is required for LIGHT-induced hypertension (systolic pressure on day 6: LIGHT = 152.3 ± 7.4 vs. LIGHT+ERW1041E [TG2 inhibitor] = 105.8 ± 13.1 or LIGHT+TG2^−/− = 114.3 ± 4.3 mm Hg, P < 0.05, n = 4–5) and renal compromise (urine albumin/creatinine: LIGHT = 0.17 ± 0.05 vs. LIGHT+ERW1041E = 0.03 ± 0.01 or LIGHT+TG2^−/− = 0.06 ± 0.01 mg/mg; plasma creatinine: LIGHT = 1.11 ± 0.04 vs. LIGHT+ERW1041E = 0.94 ± 0.04 or LIGHT+TG2^−/− = 0.88 ± 0.09 mg/dl; urine volume: LIGHT = 0.23 ± 0.1 vs. LIGHT+ERW1041E = 0.84 ± 0.13 or LIGHT+TG2^−/− = 1.02 ± 0.09 ml/24 hour on day 14, P < 0.05, n = 4–5). Our mechanistic studies showed that the TG2-mediated AT₁R modification and accumulation (relative renal AT₁R level: phosphate-buffered saline [PBS] = 1.23 ± 0.22, LIGHT = 3.49 ± 0.37, and LIGHT+ERW1041E = 1.77 ± 0.46, P < 0.05, n = 3; LIGHT+TG2^+/+ = 85.28 ± 36.11 vs. LIGHT+TG2^−/− = 7.01 ± 5.68, P < 0.05, n = 3) induced by LIGHT is associated with abrogated β-arrestin binding (AT₁R/associated β-arrestin ratio: PBS = 2.62 ± 1.07, LIGHT = 38.60 ± 13.91, and LIGHT+ERW1041E = 6.97 ± 2.91, P < 0.05, n = 3; LIGHT+TG2^+/+ = 66.43 ± 44.81 vs. LIGHT+TG2^−/− = 2.45 ± 1.78, P < 0.01, n = 3) and could be found in renal medulla tubules of kidneys (relative tubular AT₁R level: PBS = 5.91 ± 2.93, LIGHT = 92.82 ± 19.54, LIGHT+ERW1041E = 28.49 ± 11.65, and LIGHT+TG2^−/− = 0.14 ± 0.10, P < 0.01, n = 5) and the blood vasculature (relative vascular AT₁R level: PBS = 0.70 ± 0.30, LIGHT = 13.75 ± 2.49, and LIGHT+ERW1041E = 3.28 ± 0.87, P < 0.01, n = 3), 2 of the tissues highly related to the genesis of hypertension. Our in vitro cellular assays showed that LIGHT stimulation triggered a rapid TG2-dependent increase in the abundance of AT₁Rs (relative AT₁R level after 2-hour LIGHT treatment: AT₁R (WT)+TG2 = 2.21 ± 0.23, AT₁R (Q315A)+TG2 = 0.18 ± 0.23, P < 0.05 vs. starting point = 1, n = 2) and downstream calcium signaling (fold increase in NFAT-driven luciferase activity: Saline = 0.02 ± 0.03, Ang II = 0.17 ± 0.08, LIGHT = 0.05 ± 0.04, LIGHT+Ang II = 0.90 ± 0.04 (P < 0.01 vs. Ang II), and LIGHT+Ang II+ERW1041E = 0.15 ± 0.15 (P < 0.01 vs. LIGHT+Ang II), n = 3).

CONCLUSIONS

Our data indicate an essential and systemic role for TG2 in bridging inflammation to hypertension via its posttranslational modifications stabilizing AT₁ receptor and sensitizing Ang II. Our findings also suggest that TG2 inhibitors could be used as a novel group of cardiovascular agents.

Angiotensin II-induced hypertension and cardiac hypertrophy are differentially mediated by TLR3- and TLR4-dependent pathways

Toll-like receptors (TLR) are key components of the innate immune system that elicit inflammatory responses through the adaptor proteins myeloid differentiation protein 88 (MyD88) and Toll-interleukin receptor domain-containing adaptor protein-inducing interferon-β (TRIF). Previously, we demonstrated that TRIF mediates the signaling of angiotensin II (ANG II)- induced hypertension and cardiac hypertrophy. Since TRIF is activated selectively by TLR3 and TLR4, our goals in this study were to determine the roles of TLR3 and TLR4 in mediating ANG II-induced hypertension and cardiac hypertrophy, and associated changes in proinflammatory gene expression in heart and kidney. In wild-type (WT) mice, ANG II infusion (1,000 ng·kg^-1·min^-1 for 3 wk) increased systolic blood pressure and caused cardiac hypertrophy. In ANG II-infused TLR4-deficient mice (Tlr4^del), hypertrophy was significantly attenuated despite a preserved or enhanced hypertensive response. In contrast, in TLR3-deficient mice (Tlr3^-/-), both ANG II-induced hypertension and hypertrophy were abrogated. In WT mice, ANG II increased the expression of several proinflammatory genes in hearts and kidneys that were attenuated in both TLR4- and TLR3-deficient mice compared with WT. We conclude that ANG II activates both TLR4-TRIF and TLR3-TRIF pathways in a nonredundant manner whereby hypertension is dependent on activation of the TLR3-TRIF pathway and cardiac hypertrophy is dependent on both TLR3-TRIF and TLR4-TRIF pathways. NEW & NOTEWORTHY Angiotensin II (ANG II)-induced hypertension is dependent on the endosomal Toll-like receptor 3 (TLR3)-Toll-interleukin receptor domain-containing adaptor protein-inducing interferon-β (TRIF) pathway of the innate immune system but not on cell membrane localized TLR4. However, ANG II-induced cardiac hypertrophy is regulated by both TLR4-TRIF and TLR3-TRIF pathways. Thus, ANG II-induced rise in systolic blood pressure is independent of TLR4-TRIF effect on cardiac hypertrophy. The TLR3-TRIF pathway may be a potential target of therapeutic intervention.

Inflammation, Autoimmunity, and Hypertension: The Essential Role of Tissue Transglutaminase

Inflammatory cytokines cause hypertension when introduced into animals. Additional evidence indicates that cytokines induce the production of autoantibodies that activate the AT1 angiotensin receptor (AT1R). Extensive evidence shows that these autoantibodies, termed AT1-AA, contribute to hypertension. We review here recent studies showing that cytokine-induced hypertension and AT1-AA production require the ubiquitous enzyme, tissue transglutaminase (TG2). We consider 3 mechanisms by which TG2 may contribute to hypertension. (i) One involves the posttranslational modification (PTM) of AT1Rs at a glutamine residue that is present in the epitope sequence (AFHYESQ) recognized by AT1-AA. (ii) Another mechanism by which TG2 may contribute to hypertension is by PTM of AT1Rs at glutamine 315. Modification at this glutamine prevents ubiquitination-dependent proteasome degradation and allows AT1Rs to accumulate. Increased AT1R abundance is likely to account for increased sensitivity to Ang II activation and in this way contribute to hypertension. (iii) The increased TG2 produced as a result of elevated inflammatory cytokines is likely to contribute to vascular stiffness by modification of intracellular contractile proteins or by crosslinking vascular proteins in the extracellular matrix. This process, termed inward remodeling, results in reduced vascular lumen, vascular stiffness, and increased blood pressure. Based on the literature reviewed here, we hypothesize that TG2 is an essential participant in cytokine-induced hypertension. From this perspective, selective TG2 inhibitors have the potential to be pharmacologic weapons in the fight against hypertension.

Circulating Th1, Th2, and Th17 Levels in Hypertensive Patients

Background

Evidence from experimental studies showed that Th1, Th2, and Th17 play a pivotal role in hypertension and target organ damage. However, whether changes in the circulating Th1, Th2, and Th17 levels are associated with nondipper hypertension and carotid atherosclerotic plaque in hypertension has yet to be investigated.

Methods

Th1, Th2, and Th17 levels were detected using a flow cytometric analysis, and their related cytokines were measured by enzyme-linked immunosorbent assay in 45 hypertensive patients and 15 normotensive subjects.

Results

The frequencies of Th1 and Th17 in hypertensive patients, especially in nondipper patients and patients with carotid atherosclerotic plaque, were markedly higher than those in the control group; this was accompanied by higher IFN-γ and IL-17 levels. In contrast, the Th2 frequencies and IL-4 levels in hypertensive patients, especially in nondipper patients and patients with carotid atherosclerotic plaque, were significantly lower than those in the control group.

Conclusions

The changes in Th1, Th2, and Th17 activity are associated with the onset of the nondipper type and carotid atherosclerotic plaque in hypertensive patients.

Interleukin 17A in atherosclerosis - Regulation and pathophysiologic effector function

This review summarizes the current data on the interleukin (IL)-17A pathway in experimental atherosclerosis and clinical data. IL-17A is a prominent cytokine for early T cell response produced by both innate and adaptive leukocytes. In atherosclerosis, increased total IL-17A levels and expression in CD4⁺ T helper and γδ T cells have been demonstrated. Cytokines including IL-6 and TGFβ that increase IL-17A expression are elevated. Many other factors such as lipids, glucose and sodium chloride concentrations as well as vitamins and arylhydrocarbon receptor agonists that promote IL-17A expression are closely associated with cardiovascular risk in the human population. In acute inflammation models, IL-17A mediates innate leukocyte recruitment of both neutrophils and monocytes. In atherosclerosis, IL-17A increased aortic macrophage and T cell infiltration in most models. Secondary recruitment effects via the endothelium and according to recent data also pericytes have been demonstrated. IL-17 receptor A is highly expressed on monocytes and direct effects have been reported as well. Beyond leukocyte accumulation, IL-17A may affect other factors of plaque formation such as endothelial function, and according to some reports, fibrous cap formation and vascular relaxation with an increase in blood pressure. Anti-IL-17A agents are now available for clinical use. Cardiovascular side effect profiles are benign at this point. IL-17A appears to be a differential regulator of atherosclerosis and its effects in mouse models suggest that its modulation may have contradictory effects on plaque size and possibly stability in different patient populations.

Mechanistic rationales for targeting interleukin-17A in spondyloarthritis

The term spondyloarthritis (SpA) is used to describe a group of inflammatory autoimmune diseases, including ankylosing spondylitis and psoriatic arthritis, with common genetic risk factors and clinical features. SpA is clinically distinct from rheumatoid arthritis and typically affects the spine, sacroiliac joints, entheses, and, less commonly, peripheral joints. Although the pathogenesis of SpA is not fully understood, recent findings have identified the interleukin (IL)-17 pathway as a key mediator of disease pathogenesis. Clinical evidence for the efficacy of IL-17A inhibition by biologic agents was initially shown in patients with chronic plaque psoriasis, another autoimmune disease mediated by the IL-17 pathway. Subsequently, similar positive efficacy for inhibition of IL-17A was seen in patients with ankylosing spondylitis and psoriatic arthritis. Inhibition of IL-17A may also improve cardiovascular and metabolic comorbidities often found in patients with SpA because studies have linked these disorders to the IL-17 pathway. In this review, we will examine key preclinical studies that demonstrated the mechanistic role of IL-17A in the development SpA and discuss how these observations were translated into clinical practice.

Inhibition of Interleukin 17-A but not Interleukin-17F Signaling Lowers Blood Pressure and Reduces End-organ Inflammation in Angiotensin II-induced Hypertension

•

Hypertension is associated with an increase in T-cell–derived cytokines such IL-17A and IL-17F.

•

Monoclonal antibodies to IL-17A, IL-17F, IL-17RA, or isotype control antibodies (IgG1) were administered twice weekly during the last 2 weeks of a 4-week angiotensin II infusion protocol in mice.

•

Antibodies to IL-17A or IL-17RA, but not IL-17F, lowered blood pressure by 30 mm Hg, attenuated renal and vascular inflammation, and reduced renal transforming growth factor beta levels (a marker of renal fibrosis) compared with control IgG1 antibodies. All 3 experimental antibodies blunted the progression of albuminuria.

•

Monoclonal antibodies to IL-17A or IL-17RA may be a useful adjunct treatment for hypertension and the associated end-organ dysfunction.

Inflammatory cytokines play a major role in the pathophysiology of hypertension. The authors previously showed that genetic deletion of interleukin (IL)-17A results in blunted hypertension and reduced renal/vascular dysfunction. With the emergence of a new class of monoclonal antibody–based drugs for psoriasis and related autoimmune disorders that target IL-17 signaling, the authors sought to determine whether these antibodies could also reduce blood pressure, renal/vascular inflammation, and renal injury in a mouse model of hypertension. The authors show that antibodies to IL-17A or the IL-17RA receptor subunit, but not IL-17F, may be a novel adjunct treatment for hypertension and the associated end-organ dysfunction.

Hypertension as an autoimmune and inflammatory disease

Hypertension that is considered idiopathic is called essential hypertension and accordingly has no clear culprit for its cause. However, basic research and clinical studies in recent years have expanded our understanding of the mechanisms underlying the development of essential hypertension. Of these, increased oxidative stress, both in the kidney and arterial wall, closely coupled with inflammatory infiltration now appear to have a prominent role. Discovery of regulatory and interleukin-17-producing T cells has enabled us to better understand the mechanism by which inflammation and autoimmunity, or autoinflammation, lead to the development of hypertension. Despite achieving considerable progress, the intricate interactions between oxidative stress, the immune system and the development of hypertension remain to be fully elucidated. In this review, we summarize recent developments in the pathophysiology of hypertension with a focus on the oxidant stress-autoimmunity-inflammation interaction.