Angiotensin-(1-7) in Paraventricular Nucleus Contributes to the Enhanced Cardiac Sympathetic Afferent Reflex and Sympathetic Activity in Chronic Heart Failure Rats

Upregulated expression of a TOR2A gene product-salusin-β in the paraventricular nucleus enhances sympathetic activity and cardiac sympathetic afferent reflex in rats with chronic heart failure induced by coronary artery ligation

AIM

Enhanced cardiac sympathetic afferent reflex (CSAR) promotes sympathetic hyperactivation in chronic heart failure (CHF). Salusin-β is a torsin family 2 member A (TOR2A) gene product and a cardiovascular active peptide closely associated with cardiovascular diseases. We aimed to determine the roles of salusin-β in the paraventricular nucleus (PVN) in modulating enhanced CSAR and sympathetic hyperactivation in rats with CHF induced by coronary artery ligation and elucidate the underlying molecular mechanisms.

METHODS

CSAR was evaluated based on the responses of mean arterial pressure (MAP) and renal sympathetic nerve activity (RSNA) to the epicardial administration of capsaicin in rats under anesthesia.

RESULTS

Salusin-β protein expression was upregulated in the PVN of the CHF compared with sham-operated rats. Salusin-β microinjection into the PVN dose-dependently increased MAP and RSNA and enhanced CSAR, while anti-salusin-β IgG exerted opposite effects. The effect of salusin-β was inhibited by reactive oxygen species (ROS) scavenger or NAD(P)H oxidase inhibitor but promoted by superoxide dismutase inhibitor. The effect of anti-salusin-β IgG was interdicted by nitric oxide (NO) synthase inhibitor. Furthermore, chronic salusin-β gene knockdown in PVN attenuated CSAR, reduced sympathetic output, improved myocardial remodeling and cardiac function, decreased NAD(P)H oxidase activity and ROS levels, and increased NO levels in the CHF rats.

CONCLUSION

Increased salusin-β activity in the PVN contributes to sympathetic hyperactivation and CSAR in CHF by inhibiting NO release and stimulating NAD(P)H oxidase-ROS production. Reducing endogenous central salusin-β expression might be a novel strategy for preventing and treating CHF in the future.

Impact of High-Dose Perindopril on Cardiac Function and Angiotensin Converting Enzyme 2/Ang-(1-9)/Ang-(1-7) in Rabbits with Ischemic Cardiac Dysfunction

Aim: To investigate the impact of high-dose of perindopril on cardiac function and ACE2/AT2R pathway in rabbits with ischemic cardiac dysfunction. Methods: The thirty rabbits with ischemic cardiac dysfunction were divided into high-dose group (Perindopril, 2 mg/kg/d), low-dose group (Perindopril, 0.66 mg/kg/d), and control groups (Saline, 2 ml/kg/d) by a random number table. After four weeks, we measured the cardiac function, The level of Ang-(1-7) and Ang-(1-9), mRNA expression level of ACE2 and AT2R. Results: The results showed that high dose and low dose of perindopril could improve cardiac function (p < 0.001), and high-dose perindopril had more significant improvement (p = 0.041). After treatment, in high-dose group, mRNA level of ACE2, AT2R in myocardium (p < 0.001) and Ang-(1-9) level in serum (p = 0.012) were higher than low-dose group, while Ang-(1-7) levels in serum didn’t show a significant difference (p = 0.829). LVEF and serum Ang-(1-9) were significantly correlated (p = 0.002), LVEF and ACE2 (p = 0.001), LVEF and AT2R (p = 0.007); however, it was no correlation between LVEF and serum Ang-(1-7) (p = 0.067). Conclusion: A high-dose of perindopril could improve ischemic cardiac dysfunction by ACE2/Ang-(1-9)/Ang-(1-7) pathway.

Angiotensin-(3-7) alleviates isoprenaline-induced cardiac remodeling via attenuating cAMP-PKA and PI3K/Akt signaling pathways

The renin-angiotensin system is involved in the regulation of various heart diseases. The present study aimed to determine the effects of angiotensin (Ang)-(3-7) on cardiac remodeling and its downstream signaling pathways in neonatal rat cardiomyocytes (NRCMs) and neonatal rat cardiac fibroblasts (NRCFs). The administration of Ang-(3-7) alleviated isoprenaline (ISO)-induced cardiac hypertrophy and fibrosis of mice. ISO treatment increased the levels of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and beta-myosin heavy chain (β-MHC) in NRCMs, and reduced the levels of collagen I, collagen III, fibronectin, and alpha-smooth muscle actin (α-SMA) in NRCFs. These changes were inhibited by Ang-(3-7) administration. The levels of protein kinase A (PKA), phosphorylated phosphatidylinositol-3-kinase (p-PI3K), and phosphorylated protein kinase B (p-Akt) were increased in NRCMs and NRCFs treated with ISO. The increase of PKA, but not p-PI3K or p-Akt was attenuated by Ang-(3-7) treatment in NRCMs. The increases of p-PI3K and p-Akt, but not PKA were reversed by Ang-(3-7) treatment in NRCFs. Treatment with cAMP or PKA overexpression reversed the attenuating effects of Ang-(3-7) on ISO-induced hypertrophy of NRCMs. The administration of PI3K inhibitor or Akt inhibitor alleviated ISO-induced fibrosis of NRCFs. These results indicated that Ang-(3-7) could alleviate cardiac remodeling. The administration of Ang-(3-7) attenuated hypertrophy of NRCMs via inhibiting the cAMP/PKA signaling pathway, and alleviated fibrosis of NRCFs via inhibiting PI3K/Akt signaling pathway.

Knockdown of Salusin-β Improves Cardiovascular Function in Myocardial Infarction-Induced Chronic Heart Failure Rats

Salusin-β is a biologically active peptide with 20 amino acids that exerts several cardiovascular activity-regulating effects, such as regulating vascular endothelial function and the proliferation of vascular smooth muscle cells. However, the regulatory effects of salusin-β in myocardial infarction-induced chronic heart failure (CHF) are still unknown. The current study is aimed at investigating the effects of silencing salusin-β on endothelial function, cardiac function, vascular and myocardial remodeling, and its underlying signaling pathways in CHF rats induced by coronary artery ligation. CHF and sham-operated (Sham) rats were subjected to tail vein injection of adenoviral vectors encoding salusin-β shRNA or a control-shRNA. The coronary artery (CA), pulmonary artery (PA), and mesenteric artery (MA) were isolated from rats, and isometric tension measurements of arteries were performed. Compared with Sham rats, the plasma salusin-β, leptin and visfatin levels and the salusin-β protein expression levels of CA, PA, and MA were increased, while the acetylcholine- (ACh-) induced endothelium-dependent vascular relaxation of CA, PA, and MA was attenuated significantly in CHF rats and was improved significantly by salusin-β gene knockdown. Salusin-β knockdown also improved cardiac function and vascular and myocardial remodeling, increased endothelial nitric oxide synthase (eNOS) activity and nitric oxide (NO) levels, and decreased NAD(P)H oxidase activity, NOX-2 and NOX-4 expression, and reactive oxygen species (ROS) levels in arteries in CHF rats. The effects of salusin-β knockdown in CHF rats were attenuated significantly by pretreatment with the NOS inhibitor L-NAME. These results indicate that silencing salusin-β contributes to the improvement of endothelial function, cardiac function, and cardiovascular remodeling in CHF by inhibiting NAD(P)H oxidase-ROS generation and activating eNOS-NO production.

Improvement of Vascular Function by Knockdown of Salusin-β in Hypertensive Rats via Nitric Oxide and Reactive Oxygen Species Signaling Pathway

Purpose

Salusin-β, a multifunctional vasoactive peptide, has a potentially important function in the pathological development of hypertension. However, the exact functional role of salusin-β and the underlying mechanism in this process are still not fully understood. The current study aimed to investigate the effects of silencing salusin-β on vascular function and vascular remodeling, as well as its signaling pathways in spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY).

Methods

Silencing salusin-β was performed by caudal vein injection of adenovirus expressing salusin-β short hairpin RNA (shRNA). Acetylcholine (ACh)-induced endothelium-dependent relaxation was used to evaluate vasodilator function, and high K⁺ solution-induced constriction was used to evaluate vasoconstriction function.

Results

Salusin-β levels in plasma and its protein expression in mesenteric artery (MA), coronary artery (CA), and pulmonary artery (PA) of SHR were higher than those in WKY. The salusin-β level and expression were decreased effectively by salusin-β shRNA. Knockdown of salusin-β decreased arterial blood pressure (ABP) and high K⁺ solution-induced vascular constrictions, and improved the endothelium-dependent relaxation and vascular remodeling in SHR. The improved effect of silencing salusin-β on ACh-induced relaxation in SHR was almost blocked by the nitric oxide synthase (NOS) inhibitor L-NAME. Compared to WKY, the endothelial NOS (eNOS) activity and level, and nitric oxide (NO) level were decreased, while NAD(P)H oxidase activity and reactive oxygen species (ROS) levels in MA, CA, and PA of SHR were increased, which were all redressed by salusin-β knockdown.

Conclusion

These results indicate that knockdown of salusin-β improves endothelium-dependent vascular relaxation and vascular remodeling and decreases ABP and vasoconstriction in SHR, which might be accomplished by increasing eNOS activation and NO release while inhibiting NAD(P)H oxidase derived-ROS generation. Scavenging salusin-β improves vascular function and then prevents the development and progression of vasculopathy of hypertension.

Neuropsychiatric Properties of the ACE2/Ang-(1-7)/Mas Pathway: A Brief Review

The current pharmacological strategies for the management of anxiety disorders and depression, serious conditions which are gaining greater prevalence worldwide, depend on only two therapeutic classes of mood-stabilizing drugs: Serotonin Reuptake Inhibitors (SSRIs) and Serotonin-Norepinephrine Reuptake Inhibitors (SNRIs). Although first line agents with proven efficacy, their clinical success in the management of anxiety disorders and depression is still considered highly complex due to the multifaceted nature of such conditions. Several studies have shown a possible therapeutic target could be found in the form of the Angiotensin-Converting Enzyme [ACE] type 2 (ACE2), Angiotensin [Ang]-(1-7) and Mas receptor pathway of the Renin- Angiotensin System (RAS), which as will be discussed, has been described to exhibit promising therapeutic properties for the management of anxiety disorders and depression. In this article, the literature to describe recent findings related to the role of the RAS in anxiety and depression disorders was briefly revised. The literature used covers a time range from 1988 to 2019 and were acquired from the National Center for Biotechnology Information's (NCBI) PubMed search engine. The results demonstrated in this review are promising and encourage the development of new research for the treatment of anxiety and depression disorders focusing on the RAS. In conclusion, the ACE2/Ang-(1-7)/Mas pathway may exhibit anxiolytic and anti-depressive effects through many possible biochemical mechanisms both centrally and peripherally, and result in highly promising mental health benefits which justifies further investigation into this system as a possible new therapeutic target in the management of neuropsychiatric disorders, including any as of yet undescribed risk-benefit analysis compared to currently-implemented pharmacological strategies.

Targeting Hypertension: Superoxide Anions are Involved in Apelininduced Long-term High Blood Pressure and Sympathetic Activity in the Paraventricular Nucleus

AIM

To determine whether apelin in paraventricular nucleus (PVN) can be a therapeutic target for hypertension.

BACKGROUND

Apelin is a specific endogenous ligand of orphan G protein-coupled receptor APJ.

OBJECTIVE

This study was designed to determine how apelin chronically regulates sympathetic nerve activity and blood pressure in PVN of rats.

METHODS

Apelin and APJ antagonist F13A were infused into PVN with osmotic minipumps. The NAD(P)H oxidase activity and superoxide anions levels in PVN of rats were determined by chemiluminescence.

RESULTS

Infusion of apelin into PVN of Wistar-Kyoto (WKY) rats induced chronic increases in systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), plasma norepinephrine (NE) level, maximal depressor response to hexamethonium (Hex), NAD(P)H oxidase activity, superoxide anions levels, and Nox4 expression. Infusion of F13A into PVN of spontaneously hypertensive rats (SHRs) caused chronic decreases in SBP, DBP, MAP, plasma NE level, maximal depressor response to Hex, NAD(P)H oxidase activity, and superoxide anions levels. Hex, a sympathetic ganglion blocker, inhibited apelin-induced increases in SBP, DBP and MAP. SOD overexpression in PVN of SHRs inhibited the apelin-induced increase in SBP, DBP, MAP, plasma NE level, and maximal depressor response to Hex. PVN Nox4 knockdown also attenuated the apelin-induced increase in SBP, DBP, MAP, plasma NE level, and maximal depressor response to Hex. Chronic injection of F13A into PVN reduced fibrosis of renal artery, thoracic aorta, and heart in SHRs.

CONCLUSION

These results demonstrated that in PVN apelin induced long-term high blood pressure and sympathetic activity via increasing oxidative stress.

The emerging role of cell senescence in atherosclerosis

Cell senescence is a fundamental mechanism of aging and appears to play vital roles in the onset and prognosis of cardiovascular disease, fibrotic pulmonary disease, liver disease and tumor. Moreover, an increasing body of evidence shows that cell senescence plays an indispensable role in the formation and development of atherosclerosis. Multiple senescent cell types are associated with atherosclerosis, senescent human vascular endothelial cells participated in atherosclerosis via regulating the level of endothelin-1 (ET-1), nitric oxide (NO), angiotensin II and monocyte chemoattractant protein-1 (MCP-1), senescent human vascular smooth muscle cells-mediated plaque instability and vascular calcification via regulating the expression level of BMP-2, OPN, Runx-2 and inflammatory molecules, and senescent macrophages impaired cholesterol efflux and promoted the development of senescent-related cardiovascular diseases. This review summarizes the characteristics of cell senescence and updates the molecular mechanisms underlying cell senescence. Moreover, we also discuss the recent advances on the molecular mechanisms that can potentially regulate the development and progression of atherosclerosis.

A TOR2A Gene Product: Salusin-β Contributes to Attenuated Vasodilatation of Spontaneously Hypertensive Rats

PURPOSE

Attenuated vasodilatation of small arteries is a hallmark feature of hypertension. Salusin-β, which is a TOR2A gene product and an important vasoactive peptide, has a close relationship with cardiovascular disease. This study aimed to determinate the roles of salusin-β in vasodilatation, and its signal pathways in Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR).

METHODS

Isometric tension experiments were performed. Vasodilatation was induced by acetylcholine (ACh) or sodium nitroprusside (SNP).

RESULTS

Plasma salusin-β levels and their protein expressions in coronary artery (CA), mesenteric artery (MA), and pulmonary artery (PA) of SHR were much higher than that of WKY. Intravenous injection of salusin-β increased arterial blood pressure in SHR, while anti-salusin-β IgG decreased it. Salusin-β further deteriorated, while anti-salusin-β IgG improved, the attenuated ACh-induced relaxation, the decreased nitric oxide (NO) level, and endothelial nitric oxide synthase (eNOS) activity in arteries of SHR, and salusin-β had no significant effect on SNP-induced relaxation. The NAD(P)H oxidase activity and reactive oxygen species (ROS) level in arteries of SHR were much higher than that of WKY, which was further increased by salusin-β but reduced by anti-salusin-β IgG. ROS scavenger NAC or antioxidant apocynin significantly inhibited, while SOD inhibitor DETC aggravated, the effects of salusin-β, and the eNOS inhibitor L-NAME inhibited the effects of anti-salusin-β IgG.

CONCLUSIONS

These results indicated that enhanced salusin-β activity is involved in attenuated endothelium-dependent vasodilatation pathogenesis in SHR by activating NAD(P)H oxidase derived ROS generation and inhibiting eNOS activation and NO release.

Effects of Angiotensin-(1-7) and Angiotensin II on Acetylcholine-Induced Vascular Relaxation in Spontaneously Hypertensive Rats

Endothelial dysfunction of small arteries occurs in patients with hypertension and in various hypertensive models. Endothelial function is usually evaluated by the degree of acetylcholine- (ACh-) induced vascular relaxation. Our previous study has found that compared to Wistar-Kyoto rats (WKY), ACh-induced vasodilatation was attenuated significantly in the mesenteric artery (MA), coronary artery (CA), and pulmonary artery (PA) of spontaneously hypertensive rats (SHR). This study investigated the influence of angiotensin- (Ang-) (1-7) and Ang II on blood pressure and ACh-induced vascular relaxation, as well as their interactive roles and downstream signal pathways in SHR and WKY. Intravenous injection of Ang II significantly increased, while Ang-(1-7) decreased the mean arterial pressure (MAP) in SHR. Ang-(1-7) improved ACh-induced relaxation in the MA, CA, and PA of SHR, while Ang II further attenuated it, which were inhibited by pretreatment with Mas receptor antagonist A-779 or AT₁ receptor antagonist losartan, respectively. Ang-(1-7) decreased the basal arterial tension, and Ang II induced great vasoconstriction in SHR. Pretreatment with Ang-(1-7) inhibited the Ang II-induced pressor response, vasoconstriction, and the effects on ACh-induced relaxation in SHR. AT₁ receptor expression was higher, while nitric oxide (NO), cGMP, and protein kinase G (PKG) levels of arteries were lower in SHR than in WKY. Ang II decreased, while Ang-(1-7) increased, the levels of NO, cGMP, and PKG of arteries. In addition, pretreatment with Ang-(1-7) inhibited the Ang II-induced reduction of NO, cGMP, and PKG in SHR. These results indicate that the activation of the Mas receptor by Ang-(1-7) can improve endothelial function and decrease MAP in SHR and inhibit the deteriorative effect of Ang II on endothelial function through the NO-cGMP-PKG pathway.

Intermedin in Paraventricular Nucleus Attenuates Ang II-Induced Sympathoexcitation through the Inhibition of NADPH Oxidase-Dependent ROS Generation in Obese Rats with Hypertension

Increased reactive oxygen species (ROS) induced by angiotensin II (Ang II) in the paraventricular nucleus (PVN) play a critical role in sympathetic overdrive in hypertension (OH). Intermedin (IMD), a bioactive peptide, has extensive clinically prospects in preventing and treating cardiovascular diseases. The study was designed to test the hypothesis that IMD in the PVN can inhibit the generation of ROS caused by Ang II for attenuating sympathetic nerve activity (SNA) and blood pressure (BP) in rats with obesity-related hypertension (OH). Male Sprague-Dawley rats (160-180 g) were used to induce OH by feeding of a high-fat diet (42% kcal as fat) for 12 weeks. The dynamic changes of sympathetic outflow were evaluated as the alterations of renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) responses to certain chemicals. The results showed that the protein expressions of Ang II type 1 receptor (AT1R), calcitonin receptor-like receptor (CRLR) and receptor activity-modifying protein 2 (RAMP2) and RAMP3 were markedly increased, but IMD was much lower in OH rats when compared to control rats. IMD itself microinjection into PVN not only lowered SNA, NADPH oxidase activity and ROS level, but also decreased Ang II-caused sympathetic overdrive, and increased NADPH oxidase activity, ROS levels and mitogen-activated protein kinase/extracellular signal regulated kinase (MAPK/ERK) activation in OH rats. However, those effects were mostly blocked by the adrenomedullin (AM) receptor antagonist AM22-52 pretreatment. The enhancement of SNA caused by Ang II can be significantly attenuated by the pretreatment of AT1R antagonist lorsatan, superoxide scavenger Tempol and NADPH oxidase inhibitor apocynin (Apo) in OH rats. ERK activation inhibitor U0126 in the PVN reversed Ang II-induced enhancement of SNA, and Apo and IMD pretreatment in the PVN decreased Ang II-induced ERK activation. Chronic IMD administration in the PVN resulted in significant reductions in basal SNA and BP in OH rats. Moreover, IMD lowered NADPH oxidase activity and ROS level in the PVN; reduced the protein expressions of AT1R and NADPH oxidase subunits NOX2 and NOX4, and ERK activation in the PVN; and decreased Ang II levels-inducing sympathetic overactivation. These results indicated that IMD via AM receptors in the PVN attenuates SNA and hypertension, and decreases Ang II-induced enhancement of SNA through the inhibition of NADPH oxidase activity and ERK activation.

Simultaneous determination of nine trace concentration angiotensin peptides in human serum using ultra high performance liquid chromatography with tandem mass spectrometry with sephadex LH-20 gel solid-phase extraction

The renin-angiotensin system is a highly complex enzymatic system consisting of multiple peptide hormones, enzymes, and receptors. Here, an assay to simultaneously quantify eight angiotensin peptides and bradykinin in human serum was developed and validated, using ultra high performance liquid chromatography coupled with tandem mass spectrometry. A pre-concentration method of Sephadex LH-20 gel solid-phase extraction was first applied for analysis of angiotensin peptides from serum sample. The triple quadrupole mass spectrometer was operated in the positive ion mode and multiple reaction monitoring was used for drug quantification. The analytical time was within 5 min, much raising the analysis efficiency. Limits of detection ranged from 0.9 to 1.3 pg/mL, and displayed the same level of sensitivity compared with radioimmunoassay. The method was successfully applied to 22 healthy human serum samples, giving the concentrations of angiotensin I, angiotensin II, angiotensin III, angiotensin IV, angiotensin 1-9, angiotensin 1-7, angiotensin 1-5, Asn¹ ,Val⁵ -Angiotensin II, and bradykinin for reference. This novel metabolic profile study of vasoactive peptides based on gel solid-phase extraction concentration provided not only an accurate quantitative assay of the serum concentrations, but also a promising methodology for evaluating the diagnostic values of the various peptides.

Angiotensin-(1-7) induced vascular relaxation in spontaneously hypertensive rats

Enhanced vasoconstriction and decreased vasodilatation due to endothelial dysfunction contribute to the progression of hypertension. Angiotensin (Ang)-(1-7) plays important roles in regulating the cardiovascular activity. The current study aimed to investigate the roles of Ang-(1-7) in modulating blood pressure, vascular tension and its signal pathway in spontaneously hypertensive rats (SHR). The effects of intravenous injection of drugs were determined in rats with anesthesia in vivo. Mesenteric artery (MA), coronary artery (CA) and pulmonary artery (PA) were isolated from rats and isometric tension measurements in arteries were performed. Compared with Wistar-Kyoto rats (WKY), the high K⁺ induced vasoconstriction was enhanced and acetylcholine-induced vasodilatation were attenuated in the MA, CA and PA in SHR. Intravenous injection of Ang-(1-7) decreased, while A-779 increased mean arterial pressure and abolished the hypotensive effect of Ang-(1-7) in SHR. Ang-(1-7) caused dose-dependent relaxation in MA, CA and PA in SHR, which was inhibited by pretreatment with Mas receptor antagonist A-779, nitric oxide (NO) synthase inhibitor l-NAME, guanylate cyclase inhibitor ODQ and protein kinase G (PKG) inhibitor DT-2. The Mas receptor expression, NO, cGMP and PKG levels of the three above arteries of SHR were lower than that of WKY. Ang-(1-7) increased the NO, cGMP and PKG levels in arteries from SHR, which was blocked by A-779. Activation of the Mas receptor by Ang-(1-7) relaxes the MA, CA, and PA through the NO-cGMP-PKG pathway, which contributes to the decrease of arterial pressure in SHR.

The renin-angiotensin system in cardiovascular autonomic control: recent developments and clinical implications

Complex and bidirectional interactions between the renin-angiotensin system (RAS) and autonomic nervous system have been well established for cardiovascular regulation under both physiological and pathophysiological conditions. Most research to date has focused on deleterious effects of components of the vasoconstrictor arm of the RAS on cardiovascular autonomic control, such as renin, angiotensin II, and aldosterone. The recent discovery of prorenin and the prorenin receptor have further increased our understanding of RAS interactions in autonomic brain regions. Therapies targeting these RAS components, such as angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers, are commonly used for treatment of hypertension and cardiovascular diseases, with blood pressure-lowering effects attributed in part to sympathetic inhibition and parasympathetic facilitation. In addition, a vasodilatory arm of the RAS has emerged that includes angiotensin-(1-7), ACE2, and alamandine, and promotes beneficial effects on blood pressure in part by reducing sympathetic activity and improving arterial baroreceptor reflex function in animal models. The role of the vasodilatory arm of the RAS in cardiovascular autonomic regulation in clinical populations, however, has yet to be determined. This review will summarize recent developments in autonomic mechanisms involved in the effects of the RAS on cardiovascular regulation, with a focus on newly discovered pathways and therapeutic targets for this hormone system.

Eplerenone Reverses Cardiac Fibrosis via the Suppression of Tregs by Inhibition of Kv1.3 Channel

Background: Fibroblast proliferation is a critical feature during heart failure development. Previous studies reported regulatory T-lymphocytes (Tregs)’ protective role against myocardial fibrosis. However, notably, Tregs also secrete fibrogenic cytokine TGF-β when activated. This study aimed to clarify the intriguing link between Tregs and fibrosis, the role of Tregs Kv1.3 potassium channel (regulating T-lymphocytes activation) in the fibrosis process, and how selective aldosterone receptor antagonist Eplerenone affects Tregs and fibrosis through its action on Kv1.3 channel.

Methods and Results: After co-incubation with Tregs, cardiac fibroblast proliferation (CCK-8 assay) and levels of collagen I, III, and Matrix metalloproteinase2 (ELISA) significantly elevated. Cell viability assays, Kv1.3 channel mRNA (RT-qPCR), and protein expression (In-Cell Western Blotting) revealed Tregs were activated/proliferated when co-cultured with fibroblasts. Treg intracellular TGF-β level increased by 5.8-fold, far more than that of intracellular IL-10, extracellular TGF-β and IL-10 (ELISA). And 30 μM eplerenone suppressed Tregs proliferation by 82.77% and furthermore, suppressed intracellular TGF-β level to a significantly greater extent than that of intracellular IL-10, extracellular TGF-β and IL-10. Moreover, the Kv1.3 current (whole-cell patch clamp) of Tregs in congestive heart failure patients and rats (induced by coronary artery ligation and exhaustive exercise) elevated by >4-fold than that of healthy volunteers and control rats, whereas 30 μM eplerenone suppressed the current by >60% in control Tregs. In addition, docking calculations (AutoDock software 4.0 suite) showed eplerenone has higher H-bond energy with Kv1.3 channel than other selective blockers.

Conclusion: Immuno-regulation in the late stage of CHF activates Tregs proliferation via the upregulation of Kv1.3 channels, which promotes cardiac fibrosis by primarily secreting TGF-β. Taken together, eplerenone’s high affinity to Kv1.3 channel enables it to antagonize the Kv1.3 channels directly to suppress Tregs proliferation, which in turn may play an immuno-regulatory role during CHF.

Dimerization of AT2 and Mas Receptors in Control of Blood Pressure

PURPOSE OF REVIEW

Angiotensin type 2 receptor (AT₂R) and receptor Mas (MasR) are part of the "protective arm" of the renin angiotensin system. Gene and pharmacological manipulation studies reveal that AT₂R and MasR are involved in natriuretic, vasodilatory, and anti-inflammatory responses and in lowering blood pressure in various animal models under normal and pathological conditions such as salt-sensitive hypertension, obesity, and diabetes. The scope of this review is to discuss co-localization and heterodimerization as potential molecular mechanisms of AT₂R- and MasR-mediated functions including antihypertensive activities.

RECENT FINDINGS

Accumulating evidences show that AT₂R and MasR are co-localized, make a heterodimer, and are functionally interdependent in producing their physiological responses. Moreover, ang-(1-7) preferably may be an AT₁R-biased agonist while acting as a MasR agonist. The physical interactions of AT₂R and MasR appear to be an important mechanism by which these receptors are involved in blood pressure regulation and antihypertensive activity. Whether heteromers of these receptors influence affinity or efficacy of endogenous or synthetic agonists remains a question to be considered.