The role of IL-6 in the physiologic versus hypertensive blood pressure actions of angiotensin II

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.

A novel mouse model carrying a gene trap insertion into the Hmgxb4 gene locus to examine Hmgxb4 expression in vivo

HMG (high mobility group) proteins are a diverse family of nonhistone chromosomal proteins that interact with DNA and a wide range of transcriptional regulators to regulate the structural architecture of DNA. HMGXB4 (also known as HMG2L1) is an HMG protein family member that contains a single HMG box domain. Our previous studies have demonstrated that HMGXB4 suppresses smooth muscle differentiation and exacerbates endotoxemia by promoting a systemic inflammatory response in mice. However, the expression of Hmgxb4 in vivo has not fully examined. Herein, we generated a mouse model that harbors a gene trap in the form of a lacZ gene insertion into the Hmgxb4 gene. This mouse enables the visualization of endogenous HMGXB4 expression in different tissues via staining for the β-galactosidase activity of LacZ which is under the control of the endogenous Hmgxb4 gene promoter. We found that HMGXB4 is widely expressed in mouse tissues and is a nuclear protein. Furthermore, the Hmgxb4 gene trap mice exhibit normal cardiac function and blood pressure. Measurement of β-galactosidase activity in the Hmgxb4 gene trap mice demonstrated that the arterial injury significantly induces Hmgxb4 expression. In summary, the Hmgxb4 gene trap reporter mouse described here provides a valuable tool to examine the expression level of endogenous Hmgxb4 in both physiological and pathological settings in vivo.

Molecular biochemical aspects of salt (sodium chloride) in inflammation and immune response with reference to hypertension and type 2 diabetes mellitus

Obesity, insulin resistance, type 2 diabetes mellitus (T2DM) and hypertension (HTN) are common that are associated with low-grade systemic inflammation. Diet, genetic factors, inflammation, and immunocytes and their cytokines play a role in their pathobiology. But the exact role of sodium, potassium, magnesium and other minerals, trace elements and vitamins in the pathogenesis of HTN and T2DM is not known. Recent studies showed that sodium and potassium can modulate oxidative stress, inflammation, alter the autonomic nervous system and induce dysfunction of the innate and adaptive immune responses in addition to their action on renin-angiotensin-aldosterone system. These actions of sodium, potassium and magnesium and other minerals, trace elements and vitamins are likely to be secondary to their action on pro-inflammatory cytokines IL-6, TNF-α and IL-17 and metabolism of essential fatty acids that may account for their involvement in the pathobiology of insulin resistance, T2DM, HTN and autoimmune diseases.

Causal association between periodontitis and hypertension: evidence from Mendelian randomization and a randomized controlled trial of non-surgical periodontal therapy

AIMS

Inflammation is an important driver of hypertension. Periodontitis is a chronic inflammatory disease, which could provide a mechanism for pro-hypertensive immune activation, but evidence of a causal relationship in humans is scarce. We aimed to investigate the nature of the association between periodontitis and hypertension.

METHODS AND RESULTS

We performed a two-sample Mendelian randomization analysis in the ∼750 000 UK-Biobank/International Consortium of Blood Pressure-Genome-Wide Association Studies participants using single nucleotide polymorphisms (SNPs) in SIGLEC5, DEFA1A3, MTND1P5, and LOC107984137 loci GWAS-linked to periodontitis, to ascertain their effect on blood pressure (BP) estimates. This demonstrated a significant relationship between periodontitis-linked SNPs and BP phenotypes. We then performed a randomized intervention trial on the effects of treatment of periodontitis on BP. One hundred and one hypertensive patients with moderate/severe periodontitis were randomized to intensive periodontal treatment (IPT; sub- and supragingival scaling/chlorhexidine; n = 50) or control periodontal treatment (CPT; supragingival scaling; n = 51) with mean ambulatory 24-h (ABPM) systolic BP (SBP) as primary outcome. Intensive periodontal treatment improved periodontal status at 2 months, compared to CPT. This was accompanied by a substantial reduction in mean SBP in IPT compared to the CPT (mean difference of -11.1 mmHg; 95% CI 6.5-15.8; P < 0.001). Systolic BP reduction was correlated to periodontal status improvement. Diastolic BP and endothelial function (flow-mediated dilatation) were also improved by IPT. These cardiovascular changes were accompanied by reductions in circulating IFN-γ and IL-6 as well as activated (CD38+) and immunosenescent (CD57+CD28null) CD8+T cells, previously implicated in hypertension.

CONCLUSION

A causal relationship between periodontitis and BP was observed providing proof of concept for development of clinical trial in a large cohort of hypertensive patients. ClinicalTrials.gov: NCT02131922.

Genetic polymorphisms associated with reactive oxygen species and blood pressure regulation

Hypertension is the most prevalent cause of cardiovascular disease and kidney failure, but only about 50% of patients achieve adequate blood pressure control, in part, due to inter-individual genetic variations in the response to antihypertensive medication. Significant strides have been made toward the understanding of the role of reactive oxygen species (ROS) in the regulation of the cardiovascular system. However, the role of ROS in human hypertension is still unclear. Polymorphisms of some genes involved in the regulation of ROS production are associated with hypertension, suggesting their potential influence on blood pressure control and response to antihypertensive medication. This review provides an update on the genes associated with the regulation of ROS production in hypertension and discusses the controversies on the use of antioxidants in the treatment of hypertension, including the antioxidant effects of antihypertensive drugs.

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

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

Cellular and Oxidative Mechanisms Associated with Interleukin-6 Signaling in the Vasculature

Reactive oxygen species, particularly superoxide, promote endothelial dysfunction and alterations in vascular structure. It is increasingly recognized that inflammatory cytokines, such as interleukin-6 (IL-6), contribute to endothelial dysfunction and vascular hypertrophy and fibrosis. IL-6 is increased in a number of cardiovascular diseases, including hypertension. IL-6 is also associated with a higher incidence of future cardiovascular events and all-cause mortality. Both immune and vascular cells produce IL-6 in response to a number of stimuli, such as angiotensin II. The vasculature is responsive to IL-6 produced from vascular and non-vascular sources via classical IL-6 signaling involving a membrane-bound IL-6 receptor (IL-6R) and membrane-bound gp130 via Jak/STAT as well as SHP2-dependent signaling pathways. IL-6 signaling is unique because it can also occur via a soluble IL-6 receptor (sIL-6R) which allows for IL-6 signaling in tissues that do not normally express IL-6R through a process referred to as IL-6 trans-signaling. IL-6 signaling mediates a vast array of effects in the vascular wall, including endothelial activation, vascular permeability, immune cell recruitment, endothelial dysfunction, as well as vascular hypertrophy and fibrosis. Many of the effects of IL-6 on vascular function and structure are representative of loss or reductions in nitric oxide (NO) bioavailability. IL-6 has direct effects on endothelial nitric oxide synthase activity and expression as well as increasing vascular superoxide, which rapidly inactivates NO thereby limiting NO bioavailability. The goal of this review is to highlight both the cellular and oxidative mechanisms associated with IL-6-signaling in the vascular wall in general, in hypertension, and in response to angiotensin II.

Elevated Wall Tension Initiates Interleukin-6 Expression and Abdominal Aortic Dilation

BACKGROUND

Hypertension (HTN) has long been associated with abdominal aortic aneurysm (AAA) development, and these cardiovascular pathologies are biochemically characterized by elevated plasma levels of angiotensin II (AngII) as well as interleukin-6 (IL-6). A biologic relationship between HTN and AAA has not been established, however. Accordingly, the objective of this study was to evaluate whether elevated tension may initiate IL-6 production to accumulate monocyte/macrophages and promote dilation of the abdominal aorta (AA).

METHODS

An IL-6 infusion model (4.36 μg/kg/day) was created utilizing an osmotic infusion pump, and after 4 weeks, AA diameter was measured by digital microscopy. The AA was then excised for CD68 immunostaining and flow cytometric analysis with CD11b and F4/80 to identify macrophages. Aortic segments from wild-type mice were suspended on parallel wires in an ex vivo tissue myograph at experimentally derived optimal tension (1.2 g) and in the presence of elevated tension (ET, 1.7 g) for 3 hr, and expression of IL-6 and monocyte chemoattractant protein-1 (MCP-1) was evaluated by quantitative polymerase chain reaction (QPCR). Isolated aortic vascular smooth muscle cells (VSMCs) were subjected to 12% biaxial cyclic stretch or held static (control) for 3 hr (n = 7), and IL-6 and MCP-1 expressions were evaluated by QPCR.

RESULTS

Four-week IL-6 infusion resulted in an AA outer diameter that was 72.5 ± 5.6% (P < 0.05) greater than that of control mice, and aortic dilation was accompanied by an accumulation of macrophages in the AA medial layer as defined by an increase in CD68 + staining as well as an increase by flow cytometric quantification of CD11b+/F4/80+ cells. Wild-type AA segments did not respond to ex vivo application of ET but cyclic stretch of isolated VSMCs increased IL-6 (2.03 ± 0.3 fold) and MCP-1 (1.51 ± 0.11 fold) expression compared to static control (P < 0.05). Pretreatment with the selective STAT3 inhibitor WP1066 blunted the response in both cases. Interestingly, AngII did not stimulate expression of IL-6 and MCP-1 above that initiated by tension and again, the response was inhibited by WP1066, supporting an integral role of STAT3 in this pathway.

CONCLUSIONS

An IL-6 infusion model can initiate macrophage accumulation as well as aortic dilation, and under conditions of elevated tension, this proinflammatory cytokine can be produced by aortic VSMCs. By activation of STAT3, MCP-1 is expressed to increase media macrophage abundance and create an environment susceptible to dilation. This biomechanical association between HTN and aortic dilation may allow for the identification of novel therapeutic strategies.

Role of the Immune System in Hypertension

High blood pressure is present in more than one billion adults worldwide and is the most important modifiable risk factor of death resulting from cardiovascular disease. While many factors contribute to the pathogenesis of hypertension, a role of the immune system has been firmly established by a large number of investigations from many laboratories around the world. Immunosuppressive drugs and inhibition of individual cytokines prevent or ameliorate experimental hypertension, and studies in genetically-modified mouse strains have demonstrated that lymphocytes are necessary participants in the development of hypertension and in hypertensive organ injury. Furthermore, immune reactivity may be the driving force of hypertension in autoimmune diseases. Infiltration of immune cells, oxidative stress, and stimulation of the intrarenal angiotensin system are induced by activation of the innate and adaptive immunity. High blood pressure results from the combined effects of inflammation-induced impairment in the pressure natriuresis relationship, dysfunctional vascular relaxation, and overactivity of the sympathetic nervous system. Imbalances between proinflammatory effector responses and anti-inflammatory responses of regulatory T cells to a large extent determine the severity of inflammation. Experimental and human studies have uncovered autoantigens (isoketal-modified proteins and heat shock protein 70) of potential clinical relevance. Further investigations on the immune reactivity in hypertension may result in the identification of new strategies for the treatment of the disease.

Gardenia jasminoides has therapeutic effects on L‑NNA‑induced hypertension in vivo

Gardenia jasminoides is a plant that has been used in traditional Chinese medicine. It has four key active components (genipin gentiobioside, geniposide, crocin 1 and crocin 2). The aim of the present study was to determine the anti‑hypertension effects of Gardenia jasminoidesin vivo. The chemical composition of Gardenia jasminoides was determined using liquid chromatography. The anti‑hypertensive effects of Gardenia jasminoides were determined by a L‑NG‑nitroarginine (L‑NNA)‑induced hypertension animal model. Both Gardenia jasminoides plants of the Jiangjin County variety (CJGJ) and the Lichuan City variety (HLGJ) were used. HLGJ contained more geniposide than CJGJ. L‑NNA was used to induce hypertension in mice, and the mice were subsequently treated with CJGJ and HLGJ. The Gardenia jasminoides‑treated mice exhibited lower systolic (SBP), diastolic (DBP) and mean blood pressure (MBP) than the experimental control mice. Additionally, HLGL has a more potent effect on SBP, MBP and DBP than CJGJ. Following Gardenia jasminoides treatment, the nitric oxide contents in serum, heart, liver, kidney and stomach of mice were higher than the L‑NNA‑induced control mice, and the malondialdehyde contents were lower; the levels in HLGJ‑treated mice were closer to those normal mice than the levels in CJGJ‑treated mice were. Serum levels of endothelin‑1 and vascular endothelial growth factor were reduced by HLGJ treatment in hypertensive mice, whereas the calcitonin gene‑related peptide level was raised. Reverse transcription‑polymerase chain reaction analysis of mouse heart and vessel tissue demonstrated that HLGJ‑treated mice exhibited higher heme oxygenase‑1, neuronal nitric oxide synthase (nNOS), endothelial NOS, Bax, caspase‑3, caspase‑8, caspase‑9 mRNA expression levels and lower adrenomedullin, receptor activity modifying protein, interleukin‑1β, tumor necrosis factor‑α, inducible NOS, Bcl‑2, monocyte chemoattractant protein‑1, nuclear factor‑κB and matrix metalloproteinase‑2 and ‑9 mRNA expression compared with control hypertensive mice and CJGJ‑treated mice. In conclusion, Gardenia jasminoides has anti‑hypertensive effects, and these effects may be associated with the active component, geniposide.