Angiotensin receptors in the kidney and vasculature in hypertension and kidney disease

Chronic exercise improves renal AT1 and ETB receptor functions via modulating GRK4 expression in obese Zucker rats

BACKGROUND

Physical activity has profound benefits on health, especially in patients with cardiovascular and metabolic disease. Exercise training can reduce oxidative stress, improve renal function, and thus lower blood pressure. However, the effect of exercise training on angiotensin II type 1 receptors (AT1R) and endothelin subtype B receptors (ETBR)-mediated diuresis and natriuresis in obese Zucker rats is unclear.

METHODS

Lean and obese Zucker rats were exercised or placed on a nonmoving treadmill for 8 weeks. Blood pressure was measured by tail-cuff plethysmography, and functions of AT1R and ETBR in the kidney were measured by natriuresis, respectively.

RESULTS

Our data showed that exercise training improved glucose and lipid metabolism, renal function and sodium excretion in obese Zucker rats, accompanied by decreased oxidative stress and GRK4 expression in obese Zucker rats. Moreover, exercise training reduced the Candesartan-induced an increase in diuresis and natriuresis and increased ETBR agonists (BQ3020)-mediated diuresis and natriuresis in obese Zucker rats, which were associated with decreased renal AT1R expression and ETBR phosphorylation levels.

CONCLUSIONS

The results demonstrate that exercise training lowers blood pressure via improving renal AT1R and ETBR function through modulating GRK4 expression in Obese Zucker Rats and provides potentially effective targets for obesity-related hypertension.

Star anise (Illicium verum Hook. F.) polysaccharides: Potential therapeutic management for obesity, hypertension, and diabetes

This study explores the extraction of polysaccharides from star anise (Illicium verum Hook. f.) with its anti-obesity, antihypertensive, antidiabetic, and antioxidant properties. The aim is to optimize the extraction conditions of star anise polysaccharides (SAP) utilizing propane alcohols-based deep eutectic solvents and microwave-assisted methods. The optimized conditions resulted in an extraction yield of 5.14%. The characteristics of acidic pectin-like SAP, including high viscosity (44.86 mPa s), high oil-holding capacity (14.39%), a high degree of esterification (72.53%), gel-like properties, highly amorphous, a high galacturonic acid concentration, and a highly branching size polysaccharide structure, significantly contribute to their potent inhibition of pancreatic lipase (86.67%), angiotensin-converting enzyme (73.47%), and α-glucosidase (82.33%) activities as well as to their antioxidant properties of azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS, 34.94%) and ferric ion reducing antioxidant power (FRAP, 0.56 mM FeSO4). Therefore, SAP could be used as a potential therapeutic agent for obesity, hypertension, and diabetes mellitus management.

The effect of different levels of systolic blood pressure control on new-onset chronic kidney disease in hypertension multimorbidity

To explore the effect of different levels of systolic blood pressure (SBP) control on new-onset chronic kidney disease in hypertension multimorbidity. The hypertensive patients with multimorbidity information were enrolled from the Kailuan Study. The isolated hypertension patients undergoing physical examination during the same period were selected in a 1:1 ratio as control. Finally, 12,897 participants were divided into six groups: Group SBP < 110 mmHg, Group 110 ≤ SBP < 120 mmHg, Group 120 ≤ SBP < 130 mmHg, Group 130 ≤ SBP < 140 mmHg, Group 140 ≤ SBP < 160 mmHg and Group SBP ≥ 160 mmHg. The outcomes were new-onset CKD, new onset proteinuria, decline in eGFR and high or very high risk of CKD. Cox proportional hazards regression was used to examine the hazard ratios (HRs) of the outcomes among SBP levels. When 110 ≤ SBP < 120 mmHg, the incidence density of new-onset CKD, new onset proteinuria and decline in eGFR were 59.54, 20.23 and 29.96 per 1000 person-years, respectively. Compared to this group, the HR (95% CI) values for the risk of new-onset CKD from Group SBP < 110 mmHg to Group SBP ≥ 160 mmHg were 1.03 (0.81-1.32), 1.04 (0.91-1.19), 1.09 (0.95-1.16), 1.16 (1.02-1.21) and 1.18 (1.04-1.24), respectively. For patients over 65 years old, the risks of outcomes were increased when SBP < 120 mmHg. The lowest HR of high or very high risk of CKD for participants with or without multimorbidity occurred when 120 ≤ SBP < 130 mmHg. The HR of new-onset CKD in hypertension multimorbidity was lowest at 110-120 mmHg. The optimal SBP level was between 120 and 130 mmHg for individuals with high or very high risk of CKD. For patients over 65 years old, the low limit of target BP is advised to be not lower than 120 mmHg.

The Role of Estrogen across Multiple Disease Mechanisms

Estrogen is a significant hormone that is involved in a multitude of physiological and pathological processes. In addition to its pivotal role in the reproductive system, estrogen is also implicated in the pathogenesis of a multitude of diseases. Nevertheless, previous research on the role of estrogen in a multitude of diseases, including Alzheimer's disease, depression, cardiovascular disease, diabetes, osteoporosis, gastrointestinal diseases, and estrogen-dependent cancers, has concentrated on a single disease area, resulting in a lack of comprehensive understanding of cross-disease mechanisms. This has brought some challenges to the current treatment methods for these diseases, because estrogen as a potential therapeutic tool has not yet fully developed its potential. Therefore, this review aims to comprehensively explore the mechanism of estrogen in these seven types of diseases. The objective of this study is to describe the relationship between each disease and estrogen, including the ways in which estrogen participates in regulating disease mechanisms, and to outline the efficacy of estrogen in treating these diseases in clinical practice. By studying the role of estrogen in a variety of disease mechanisms, it is hoped that a more accurate theoretical basis and clinical guidance for future treatment strategies will be provided, thus promoting the effective management and treatment of these diseases.

Gestationally administered RAS modulators reprogram endotoxic cardiovascular and inflammatory profiles in adult male offspring of preeclamptic rats

Previous studies showed that preeclampsia (PE) amplifies cardiovascular dysfunction induced by endotoxemia in adult male, but not female, offspring. Here, we asked if such aggravated endotoxic insult could be nullified by modulators of the renin-angiotensin system (RAS). PE was induced by gestational administration of Nω-nitro-L-arginine methyl ester(L-NAME, a nitric oxide synthase inhibitor). Adult male offspring of PE mothers treated gestationally with angiotensin 1-7 (Ang1-7, angiotensin II-derived vasodilator), losartan (AT1 receptor antagonist), pioglitazone (peroxisome proliferator-activated receptor gamma, PPARγ, agonist), or combined losartan/pioglitazone were instrumented with femoral indwelling catheters and challenged intravenously with a 5-mg/kg dose of lipopolysaccharides (LPS, 5 mg/kg). LPS caused significant decreases in blood pressure (BP) and spectral index of overall heart rate variability and increases in heart rate and left ventricular contractility (dP/dtmax). These effects were mostly reduced to similar magnitudes by individual drug therapies. In offspring born to Ang1-7-treated dams, the spectral index of cardiac sympathovagal balance showed elevated sympathetic dominance in response to LPS. Immunohistochemistry revealed that Ang1-7, but not losartan/pioglitazone, abolished the exaggerated increases in toll-like receptor 4 (TLR-4) expression caused by PE/LPS in heart tissues and neuronal circuits of brainstem rostral ventrolateral medulla (RVLM). By contrast, the losartan/pioglitazone regimen, but not Ang1-7, decreased and increased angiotensin converting enzyme (ACE) and ACE2 expression, respectively. Together, gestational fetal reprogramming of Ang II (depression) and Ang1-7 (activation) arms of RAS effectively counterbalance worsened endotoxic cardiovascular and inflammatory profiles in adult male offspring of PE rats.

Pulmonary hypertension and chronic kidney disease: prevalence, pathophysiology and outcomes

Pulmonary hypertension (PH) is common in patients with chronic kidney disease (CKD) or kidney failure, with an estimated prevalence of up to 78% in those referred for right-heart catheterization. PH is independently associated with adverse outcomes in CKD, raising the possibility that early detection and appropriate management of PH might improve outcomes in at-risk patients. Among patients with PH, the prevalence of CKD stages 3 and 4 is estimated to be as high as 36%, and CKD is also independently associated with adverse outcomes. However, the complex, heterogenous pathophysiology and clinical profile of CKD-PH requires further characterization. CKD is often associated with elevated left ventricular filling pressure and volume overload, which presumably leads to pulmonary vascular stiffening and post-capillary PH. By contrast, a distinct subgroup of patients at high risk is characterized by elevated pulmonary vascular resistance and right ventricular dysfunction in the absence of pulmonary venous hypertension, which may represent a right-sided cardiorenal syndrome defined in principle by hypervolaemia, salt avidity, low cardiac output and normal left ventricular function. Current understanding of CKD-PH is limited, despite its potentially important ramifications for clinical decision making. In particular, whether PH should be considered when determining the suitability and timing of kidney replacement therapy or kidney transplantation is unclear. More research is urgently needed to address these knowledge gaps and improve the outcomes of patients with or at risk of CKD-PH.

Striatin plays a major role in angiotensin II-induced cardiomyocyte and cardiac hypertrophy in mice in vivo

The three striatins (STRN, STRN3, STRN4) form the core of STRiatin-Interacting Phosphatase and Kinase (STRIPAK) complexes. These place protein phosphatase 2A (PP2A) in proximity to protein kinases thereby restraining kinase activity and regulating key cellular processes. Our aim was to establish if striatins play a significant role in cardiac remodelling associated with cardiac hypertrophy and heart failure. All striatins were expressed in control human hearts, with up-regulation of STRN and STRN3 in failing hearts. We used mice with global heterozygote gene deletion to assess the roles of STRN and STRN3 in cardiac remodelling induced by angiotensin II (AngII; 7 days). Using echocardiography, we detected no differences in baseline cardiac function or dimensions in STRN+/- or STRN3+/- male mice (8 weeks) compared with wild-type littermates. Heterozygous gene deletion did not affect cardiac function in mice treated with AngII, but the increase in left ventricle mass induced by AngII was inhibited in STRN+/- (but not STRN3+/-) mice. Histological staining indicated that cardiomyocyte hypertrophy was inhibited. To assess the role of STRN in cardiomyocytes, we converted the STRN knockout line for inducible cardiomyocyte-specific gene deletion. There was no effect of cardiomyocyte STRN knockout on cardiac function or dimensions, but the increase in left ventricle mass induced by AngII was inhibited. This resulted from inhibition of cardiomyocyte hypertrophy and cardiac fibrosis. The data indicate that cardiomyocyte striatin is required for early remodelling of the heart by AngII and identify the striatin-based STRIPAK system as a signalling paradigm in the development of pathological cardiac hypertrophy.

Recent Advances in Understanding the Molecular Pathophysiology of Angiotensin II Receptors: Lessons From Cell-Selective Receptor Deletion in Mice

The renin-angiotensin system (RAS) is an essential hormonal system involved in water and sodium reabsorption, renal blood flow regulation, and arterial constriction. Systemic stimulation of the RAS with infusion of the main peptide angiotensin II (Ang II) in animals as well as pathological elevation of renin (ie, renovascular hypertension) to increase circulatory Ang II in humans ultimately lead to hypertension and end organ damage. In addition to hypertension, accumulating evidence supports that the Ang II type 1 receptor exerts a critical role in cardiovascular and kidney diseases independent of blood pressure elevation. In the past 2 decades, the identification of an increased number of peptides and receptors has facilitated the concept that the RAS has detrimental and beneficial effects on the cardiovascular system depending on which RAS components are activated. For example, angiotensin 1-7 and Ang II type 2 receptors act as a counter-regulatory system against the classical RAS by mediating vasodilation. Although the RAS as an endocrine system for regulation of blood pressure is well established, there remain many unanswered questions and controversial findings regarding blood pressure regulation and pathophysiological regulation of cardiovascular diseases at the tissue level. This review article includes the latest knowledge gleaned from cell type-selective gene deleted mice regarding cell type-specific roles of Ang II receptors and their significance in health and diseases are discussed. In particular, we focus on the roles of these receptors expressed in vascular, cardiac, and kidney epithelial cells.

The RAAS Goodfellas in Cardiovascular System

In the last two decades, the study of the renin-angiotensin-aldosterone system (RAAS) has revealed a counterregulatory protective axis. This protective arm is characterized by ACE2/Ang 1-7/MasR and Ang 1-9 that largely counteracts the classic arm of the RAAS mediated by ACE/Ang II/AT1R/aldosterone and plays an important role in the prevention of inflammation, oxidative stress, hypertension, and cardiovascular remodeling. A growing body of evidence suggests that enhancement of this counterregulatory arm of RAAS represents an important therapeutic approach to facing cardiovascular comorbidities. In this review, we provide an overview of the beneficial effects of ACE2, Ang 1-7/MasR, and Ang 1-9 in the context of oxidative stress, vascular dysfunction, and organ damage.

Epigenetic modification in diabetic kidney disease

Diabetic kidney disease (DKD) is a common microangiopathy in diabetic patients and the main cause of death in diabetic patients. The main manifestations of DKD are proteinuria and decreased renal filtration capacity. The glomerular filtration rate and urinary albumin level are two of the most important hallmarks of the progression of DKD. The classical treatment of DKD is controlling blood glucose and blood pressure. However, the commonly used clinical therapeutic strategies and the existing biomarkers only partially slow the progression of DKD and roughly predict disease progression. Therefore, novel therapeutic methods, targets and biomarkers are urgently needed to meet clinical requirements. In recent years, increasing attention has been given to the role of epigenetic modification in the pathogenesis of DKD. Epigenetic variation mainly includes DNA methylation, histone modification and changes in the noncoding RNA expression profile, which are deeply involved in DKD-related inflammation, oxidative stress, hemodynamics, and the activation of abnormal signaling pathways. Since DKD is reversible at certain disease stages, it is valuable to identify abnormal epigenetic modifications as early diagnosis and treatment targets to prevent the progression of end-stage renal disease (ESRD). Because the current understanding of the epigenetic mechanism of DKD is not comprehensive, the purpose of this review is to summarize the role of epigenetic modification in the occurrence and development of DKD and evaluate the value of epigenetic therapies in DKD.

Novel Concepts in Nephron Sodium Transport: A Physiological and Clinical Perspective

The kidneys play a critical role in maintaining total body sodium (Na⁺) balance across a wide range of dietary intake, accomplished by a concerted effort involving multiple Na⁺ transporters along the nephron. Furthermore, nephron Na⁺ reabsorption and urinary Na⁺ excretion are closely linked to renal blood flow and glomerular filtration such that perturbations in either of them can modify Na⁺ transport along the nephron, ultimately resulting in hypertension and other Na⁺-retentive states. In this article, we provide a brief physiological overview of nephron Na⁺ transport and illustrate clinical syndromes and therapeutic agents that affect Na⁺ transporter function. We highlight recent advances in kidney Na⁺ transport, particularly the role of immune cells, lymphatics, and interstitial Na⁺ in regulating Na⁺ reabsorption, the emergence of potassium (K⁺) as a regulator of Na⁺ transport, and the evolution of the nephron to modulate Na⁺ transport.

Targeting Glomerular Hemodynamics for Kidney Protection

The kidney microcirculation is a unique structure as it is composed to 2 capillary beds in series: the glomerular and peritubular capillaries. The glomerular capillary bed is a high-pressure capillary bed, having a 60 mm Hg to 40 mm Hg pressure gradient, capable of producing an ultrafiltrate of plasma quantified as the glomerular filtration rate (GFR), thereby allowing for waste products to be removed and establishing sodium/volume homeostasis. Entering the glomerulus is the afferent arteriole, and the exiting one is the efferent arteriole. The concerted resistance of each of these arterioles is what is known as glomerular hemodynamics and is responsible for increasing or decreasing GFR and renal blood flow. Glomerular hemodynamics play an important role in how homeostasis is achieved. Minute-to-minute fluctuations in the GFR are achieved by constant sensing of distal delivery of sodium and chloride in the specialized cells called macula densa leading to upstream alternation in afferent arteriole resistance altering the pressure gradient for filtration. Specifically, 2 classes of medications (sodium glucose cotransporter-2 inhibitors and renin-angiotensin system blockers) have shown to be effective in long-term kidney health by altering glomerular hemodynamics. This review will discuss how tubuloglomerular feedback is achieved, and how different disease states and pharmacologic agents alter glomerular hemodynamics.

Berry consumption mitigates the hypertensive effects of a high-fat, high-sucrose diet via attenuation of renal and aortic AT1R expression resulting in improved endothelium-derived NO bioavailability

Dysregulation of the renin-angiotensin system (RAS) is a contributor to high-fat diet-related blood pressure (BP) increases. Deleterious effects of dysregulated RAS result in an overproduction of reactive oxygen species and a decrease in endothelial nitric oxide (NO) bioavailability due to increased NADPH oxidase (NOX) expression. Dietary polyphenols have been shown to mitigate the imbalance in the redox state and protect against endothelial dysfunction induced by a high-fat diet. Thus, we aim to determine whether polyphenol-rich blackberry and raspberry, alone and in combination, attenuate the detrimental effects of a high-fat, high-sucrose (HFHS) diet on the vascular endothelium and kidneys of mice. We show that a HFHS diet increased the expression of renal and aortic angiotensin type 1 receptor (AT₁R). Further, NOX1 and NOX4 expression were increased in the kidney contributing to fibrotic damage. In human aortic endothelial cells (HAECs), palmitic acid increased the expression of NOX4, potentially driving oxidative damage in the aorta, as evidenced by increased nitrotyrosine expression. Berries reduced the expression of renal and aortic AT₁R, leading to a subsequent decrease in renal NOX expression and reduced aortic oxidative stress evidenced by reduced nitrotyrosine expression. Blackberry and raspberry in combination increased the expression of NRF2 and its downstream proteins in HAECs, thereby reducing the oxidative burden to the endothelium. In combination, blackberry and raspberry also increased serum levels of NO metabolites. These findings indicate that blackberry and raspberry unique polyphenols may act synergistically to favorably modulate the abovementioned pathways and attenuate HFHS diet-induced increases in BP.

Role of sex hormones in diabetic nephropathy

Diabetic nephropathy (DN) is the most common microvascular complication in diabetes and one of the leading causes of end-stage renal disease. The standard treatments for patients with classic DN focus on blood glucose and blood pressure control, but these treatments can only slow the progression of DN instead of stopping or reversing the disease. In recent years, new drugs targeting the pathological mechanisms of DN (e.g., blocking oxidative stress or inflammation) have emerged, and new therapeutic strategies targeting pathological mechanisms are gaining increasing attention. A growing number of epidemiological and clinical studies suggest that sex hormones play an important role in the onset and progression of DN. Testosterone is the main sex hormone in males and is thought to accelerate the occurrence and progression of DN. Estrogen is the main sex hormone in females and is thought to have renoprotective effects. However, the underlying molecular mechanism by which sex hormones regulate DN has not been fully elucidated and summarized. This review aims to summarize the correlation between sex hormones and DN and evaluate the value of hormonotherapy in DN.

Genetic Polymorphism in Angiotensinogen and Its Association with Cardiometabolic Diseases

Angiotensinogen (AGT) is one of the most significant enzymes of the renin-angiotensin-aldosterone system (RAAS) which is involved in the regulation and maintenance of blood pressure. AGT is involved in the production of angiotensin I which is then converted into angiotensin II that leads to renal homeostasis. However, various genetic polymorphisms in AGT have been discovered in recent times which have shown an association with various diseases. Genetic polymorphism increases the level of circulating AGT in blood which exaggerates the effects produced by AGT. The associated diseases occur due to various effects produced by increased AGT levels. Several cardiovascular diseases including myocardial infarction, coronary heart disease, heart failure, hypertrophy, etc. are associated with AGT polymorphism. Other diseases such as depression, obesity, diabetic nephropathy, pre-eclampsia, and liver injury are also associated with some variants of AGT gene. The most common variants of AGT polymorphism are M235T and T174M. The two variants are associated with many diseases. Some other variants such as G-217A, A-6G, A-20C and G-152A, are also present but they are not as significant as that of M235T and T174M variants. These variants increase the level of circulating AGT and are associated with prevalence of different diseases. These diseases occur through various pathological pathways, but the initial reason remains the same, i.e., increased level of AGT in the blood. In this article, we have majorly focused on how genetic polymorphism of different variants of AGT gene is associated with the prevalence of different diseases.

The complicated lives of GPCRs in cardiac fibroblasts

The role of different G protein-coupled receptors (GPCRs) in the cardiovascular system is well understood in cardiomyocytes and vascular smooth muscle cells (VSMCs). In the former, stimulation of Gs-coupled receptors leads to increases in contractility, while stimulation of Gq-coupled receptors modulates cellular survival and hypertrophic responses. In VSMCs, stimulation of GPCRs also modulates contractile and cell growth phenotypes. Here, we will focus on the relatively less well studied effects of GPCRs in cardiac fibroblasts, focusing on key signalling events involved in the activation and differentiation of these cells. We also review the hierarchy of signalling events driving the fibrotic response and the communications between fibroblasts and other cells in the heart. We discuss how such events may be distinct depending on where the GPCRs and their associated signalling machinery are localized in these cells with an emphasis on nuclear membrane-localized receptors. Finally, we explore what such connections between cell surface and nuclear GPCR signalling might mean for cardiac fibrosis.

Mediterranean G6PD variant rats are protected from Angiotensin II-induced hypertension and kidney damage, but not from inflammation and arterial stiffness

RATIONALE

Epidemiological studies suggest that individuals in the Mediterranean region with deficiency of glucose-6-phosphate dehydrogenase (G6PD) are less susceptible to cardiovascular diseases. However, our knowledge regarding the effects of G6PD deficiency on pathogenesis of vascular diseases caused by factors, like angiotensin II (Ang-II), which stimulate synthesis of inflammatory cytokines and vascular inflammation, is lacking. Furthermore, to-date the effect of G6PD deficiency on vascular health has been controversial and difficult to experimentally prove due to a lack of good animal model.

OBJECTIVE

To determine the effect of Ang-II-induced hypertension (HTN) and stiffness in a rat model of the Mediterranean G6PD (G6PD^S188F) variant and in wild-type (WT) rats.

METHODS AND RESULTS

Our findings revealed that infusion of Ang-II (490 ng/kg/min) elicited less HTN and medial hypertrophy of carotid artery in G6PD^S188F than in WT rats. Additionally, Ang-II induced less glomerular and tubular damage in the kidneys - a consequence of elevated pressure - in G6PD^S188F than WT rats. However, Ang-II-induced arterial stiffness increased in G6PD^S188F and WT rats, and there were no differences between the groups. Mechanistically, we found aorta of G6PD^S188F as compared to WT rats produced less sustained contraction and less inositol-1,2,3-phosphate (IP3) and superoxide in response to Ang-II. Furthermore, aorta of G6PD^S188F as compared to WT rats expressed lower levels of phosphorylated extracellular-signal regulated kinase (ERK). Interestingly, the aorta of G6PD^S188F as compared to WT rats infused with Ang-II transcribed more (50-fold) myosin heavy chain-11 (MYH11) gene, which encodes contractile protein of smooth muscle cell (SMC), and less (2.3-fold) actin-binding Rho-activating gene, which encodes a protein that enhances SMC proliferation. A corresponding increase in MYH11 and Leiomodin-1 (LMOD1) staining was observed in arteries of Ang-II treated G6PD^S188F rats. However, G6PD deficiency did not affect the accumulation of CD45⁺ cells and transcription of genes encoding interleukin-6 and collagen-1a1 by Ang-II.

CONCLUSIONS

The G6PD^S188F loss-of-function variant found in humans protected rats from Ang-II-induced HTN and kidney damage, but not from vascular inflammation and arterial stiffness.