Angiotensin II Type 1 Receptor Research Articles

A loss-of-function AGTR1 variant in a critically-ill infant with renal tubular dysgenesis: case presentation and literature review

BackgroundRenal tubular dysgenesis (RTD) is a severe disorder with poor prognosis significantly impacting the proximal tubules of the kidney while maintaining an anatomically normal gross structure. The genetic origin of RTD, involving variants in the ACE, REN, AGT, and AGTR1 genes, affects various enzymes or receptors within the Renin angiotensin system (RAS). This condition manifests prenatally with oligohydramninos and postnatally with persistent anuria, severe refractory hypotension, and defects in skull ossification.Case presentationIn this report, we describe a case of a female patient who, despite receiving multi vasopressor treatment, experienced persistent hypotension, ultimately resulting in early death at five days of age. While there was a history of parental consanguinity, no reported family history of renal disease existed. Blood samples from the parents and the remaining DNA sample of the patient underwent Whole Genome Sequencing (WGS). The genetic analysis revealed a rare homozygous loss of function variant (NM_000685.5; c.415C > T; p.Arg139*) in the Angiotensin II Receptor Type 1 (AGTR1) gene.ConclusionThis case highlights the consequence of loss-of-function variants in AGTR1 gene leading to RTD, which is characterized by high mortality rate at birth or during the neonatal period. Furthermore, we provide a comprehensive review of previously reported variants in the AGTR1 gene, which is the least encountered genetic cause of RTD, along with their associated clinical features.

Droplet-based microfluidic platform for detecting agonistic peptides that are self-secreted by yeast expressing a G-protein-coupled receptor

BackgroundSingle-cell droplet microfluidics is an important platform for high-throughput analyses and screening because it provides an independent and compartmentalized microenvironment for reaction or cultivation by coencapsulating individual cells with various molecules in monodisperse microdroplets. In combination with microbial biosensors, this technology becomes a potent tool for the screening of mutant strains. In this study, we demonstrated that a genetically engineered yeast strain that can fluorescently sense agonist ligands via the heterologous expression of a human G-protein-coupled receptor (GPCR) and concurrently secrete candidate peptides is highly compatible with single-cell droplet microfluidic technology for the high-throughput screening of new agonistically active peptides.ResultsThe water-in-oil microdroplets were generated using a flow-focusing microfluidic chip to encapsulate engineered yeast cells coexpressing a human GPCR [i.e., angiotensin II receptor type 1 (AGTR1)] and a secretory agonistic peptide [i.e., angiotensin II (Ang II)]. The single yeast cells cultured in the droplets were then observed under a microscope and analyzed using image processing incorporating machine learning techniques. The AGTR1-mediated signal transduction elicited by the self-secreted Ang II peptide was successfully detected via the expression of a fluorescent reporter in single-cell yeast droplet cultures. The system could also distinguish Ang II analog peptides with different agonistic activities. Notably, we further demonstrated that the microenvironment of the single-cell droplet culture enabled the detection of rarely existing positive (Ang II-secreting) yeast cells in the model mixed cell library, whereas the conventional batch-culture environment using a shake flask failed to do so. Thus, our approach provided compartmentalized microculture environments, which can prevent the diffusion, dilution, and cross-contamination of peptides secreted from individual single yeast cells for the easy identification of GPCR agonists.ConclusionsWe established a droplet-based microfluidic platform that integrated an engineered yeast biosensor strain that concurrently expressed GPCR and self-secreted the agonistic peptides. This offers individually isolated microenvironments that allow the culture of single yeast cells secreting these peptides and gaging their signaling activities, for the high-throughput screening of agonistic peptides. Our platform base on yeast GPCR biosensors and droplet microfluidics will be widely applicable to metabolic engineering, environmental engineering, and drug discovery.

The 2023 Lewis K. Dahl Memorial Lecture: Angiotensin-Converting Enzyme 2 Posttranslational Modifications-Implications for Hypertension and SARS-CoV-2 Infection.

ACE2 (angiotensin-converting enzyme 2), a multifunctional transmembrane protein, is well recognized as an important member of the (RAS) renin-angiotensin system with important roles in the regulation of cardiovascular function by opposing the harmful effects of Ang-II (angiotensin II) and AT1R (Ang-II type 1 receptor) activation. More recently, ACE2 was found to be the entry point for the SARS-CoV-2 virus into cells, causing COVID-19. This finding has led to an exponential rise in the number of publications focused on ACE2, albeit these studies often have opposite objectives to the preservation of ACE2 in cardiovascular regulation. However, notwithstanding accumulating data of the role of ACE2 in the generation of angiotensin-(1-7) and SARS-CoV-2 internalization, numerous other putative roles of this enzyme remain less investigated and not yet characterized. Currently, no drug modulating ACE2 function or expression is available in the clinic, and the development of new pharmacological tools should attempt targeting each step of the lifespan of the protein from synthesis to degradation. The present review expands on our presentation during the 2023 Lewis K. Dahl Memorial Lecture Sponsored by the American Heart Association Council on Hypertension. We provide a critical summary of the current knowledge of the mechanisms controlling ACE2 internalization and intracellular trafficking, the mutual regulation with GPCRs (G-protein-coupled receptors) and other proteins, and posttranslational modifications. A major focus is on ubiquitination which has become a critical step in the modulation of ACE2 cellular levels.

Reduced cardiac antioxidant defenses mediate increased susceptibility to workload-induced myocardial injury in males with genetic cardiomyopathy

Ongoing cardiomyocyte injury is a major mechanism in the progression of heart failure, particularly in dystrophic hearts. Due to the poor regenerative capacity of the adult heart, cardiomyocyte death results in the permanent loss of functional myocardium. Understanding the factors contributing to myocyte injury is essential for the development of effective heart failure therapies. As a model of persistent cardiac injury, we examined mice lacking β-sarcoglycan (β-SG), a key component of the dystrophin glycoprotein complex (DGC). The loss of the sarcoglycan complex markedly compromises sarcolemmal integrity in this β-SG−/− model. Our studies aim to characterize the mechanisms underlying dramatic sex differences in susceptibility to cardiac injury in β-SG−/− mice. Male β-SG−/− hearts display significantly greater myocardial injury and death following isoproterenol-induced cardiac stress than female β-SG−/− hearts. This protection of females was independent of ovarian hormones. Male β-SG−/− hearts displayed increased susceptibility to exogenous oxidative stress and were significantly protected by angiotensin II type 1 receptor (AT1R) antagonism. Increasing general antioxidative defenses or increasing the levels of S-nitrosylation both provided protection to the hearts of β-SG−/− male mice. Here we demonstrate that increased susceptibility to oxidative damage leads to an AT1R-mediated amplification of workload-induced myocardial injury in male β-SG−/− mice. Improving oxidative defenses, specifically by increasing S-nitrosylation, provided protection to the male β-SG−/− heart from workload-induced injury. These studies describe a unique susceptibility of the male heart to injury and may contribute to the sex differences in other forms of cardiac injury.

The angiotensin II type 1 receptor mediates the induction of oxidative stress, apoptosis, and autophagy in HUVECs induced by angiotensin II

Angiotensin (Ang) II, which is the central effector of the renin-angiotensin system (RAS), is one of the principal mediators of vascular dysfunction in hypertension and cardiovascular diseases. Proper vascular function is mediated by oxidative stress, cell apoptosis, and autophagy. However, the underlying signaling pathways and the major RAS components involved in this process are still not fully understood. In the present study, the effect of Ang II on reactive oxygen species (ROS) production, apoptosis induction, and autophagy in human umbilical vein endothelial cells (HUVECs) was investigated. An Annexin V kit was used for the apoptosis analysis, and caspase-3/7 activities were measured with the Caspase-Glo 3/7 Assay Kit. ROS production was measured using a 2,7-dichlorodihydrofluorescein diacetate probe whereas detection of autophagy was performed using acridine orange staining. We found that Ang II increases oxidative stress via ROS production, cell apoptosis via caspase 3/7, and the mitochondrial membrane potential (MMP). Interestingly, losartan, being an antagonist of the angiotensin II type 1 receptor (AT1R), has demonstrated the ability to restore autophagy levels to that of the control group subsequent to its induction by Ang II. The latter can thus induce endothelial cell damage, through excessive oxidative stress and defective autophagy-related apoptosis, which can be inhibited by losartan. These findings reinforce the pivotal role played by the Ang II/AT1R axis in the pathogenesis of vascular damage and bolster our knowledge of the role played by ROS/autophagy-related apoptosis via AT1R in the pathogenesis of hypertension and vascular diseases.

Angiotensin II type-2 receptor signaling facilitates liver injury repair and regeneration via inactivation of Hippo pathway.

The angiotensin II type 2 receptor (AT2R) is a well-established component of the renin-angiotensin system and is known to counteract classical activation of this system and protect against organ damage. Pharmacological activation of the AT2R has significant therapeutic benefits, including vasodilation, natriuresis, anti-inflammatory activity, and improved insulin sensitivity. However, the precise biological functions of the AT2R in maintaining homeostasis in liver tissue remain largely unexplored. In this study, we found that the AT2R facilitates liver repair and regeneration following acute injury by deactivating Hippo signaling and that interleukin-6 transcriptionally upregulates expression of the AT2R in hepatocytes through STAT3 acting as a transcription activator binding to promoter regions of the AT2R. Subsequently, elevated AT2R levels activate downstream signaling via heterotrimeric G protein Gα12/13-coupled signals to induce Yap activity, thereby contributing to repair and regeneration processes in the liver. Conversely, a deficiency in the AT2R attenuates regeneration of the liver while increasing susceptibility to acetaminophen-induced liver injury. Administration of an AT2R agonist significantly enhances the repair and regeneration capacity of injured liver tissue. Our findings suggest that the AT2R acts as an upstream regulator in the Hippo pathway and is a potential target in the treatment of liver damage.

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

ABSTRACT 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.

Combined vaccines against angiotensin II receptor type 1 and alpha 1D-adrenergic receptor for hypertension.

Compared with monotherapy, combination therapy with multiple antihypertensive drugs has demonstrated superior efficacy in the management of hypertension. The aim of this study was to explore the efficacy of multitarget combined vaccines in achieving simultaneous antihypertensive and target organ protection effects. Our team has developed ATRQβ-001 and ADRQβ-004 vaccines targeting Ang II type 1 receptor (AT1R) and α1D-adrenergic receptor (α1D-AR), respectively. In NG-nitroarginine methyl ester (l-NAME) + abilities spontaneously hypertensive rats (SHRs) model, SHRs were simultaneously inoculated with ATRQβ-001 and ADRQβ-004 vaccines. Histological and biochemical analyses were performed to evaluate the antihypertensive effects and target organ protection of the ATRQβ-001 and ADRQβ-004 combined vaccines in comparison with those of the single vaccine. Both ATRQβ-001 and ADRQβ-004 vaccines induced robust antibody production, resulting in persistent high antibody titers in rats. Notably, the combined administration of both vaccines significantly decreased SBP in SHRs compared with treatment with a single vaccine, both before and after l-NAME administration. Furthermore, the combined vaccine regimen demonstrated superior efficacy in protecting against vascular remodeling, myocardial hypertrophy and fibrosis, and kidney injury in SHRs. Mechanistically, the combined vaccines exhibited significantly downregulated the expression of angiotensin II type 1 receptor (AT1R) and α1D-adrenergic receptor (α1D-AR). Importantly, no apparent immune-related adverse effects were observed in animals immunized with the combined vaccines. Preliminary findings from this investigation suggest that co-administration of the novel ATRQβ-001 and ADRQβ-004 vaccines holds potential as a groundbreaking therapeutic strategy for managing hypertension.Graphical abstract: http://links.lww.com/HJH/C436.

Bidirectional relation between dipeptidyl peptidase 4 and angiotensin II type I receptor signaling.

Cardiometabolic diseases are often associated with heightened levels of angiotensin II (Ang II), which accounts for the observed oxidative stress, inflammation, and fibrosis. Accumulating evidence indicates a parallel upregulation of dipeptidyl dipeptidase 4 (DPP4) activity in cardiometabolic diseases, with its inhibition shown to mitigate oxidative stress, inflammation, and fibrosis. These findings highlight an overlap between the pathophysiological mechanisms used by Ang II and DPP4. Recent evidence demonstrates that targeted inhibition of DPP4 prevents the rise in Ang II and its associated molecules in experimental models of cardiometabolic diseases. Similarly, inhibitors of the angiotensin I-converting enzyme (ACE) or Ang II type 1 receptor (AT1R) blockers downregulate DPP4 activity, establishing a bidirectional relationship between DPP4 and Ang II. Here, we discuss the current evidence supporting the cross talk between Ang II and DPP4, along with the potential mechanisms promoting this cross regulation. A comprehensive analysis of this bidirectional relationship across tissues will advance our understanding of how DPP4 and Ang II collectively promote the development and progression of cardiometabolic diseases.

Piper sarmentosum Roxb. Inhibits Angiotensin-Converting Enzyme Activity in Phorbol 12-Myristate-13-Acetate-Induced Endothelial Cells.

Angiotensin-converting enzyme (ACE) plays a crucial role in the pathogenesis of hypertension. Piper sarmentosum Roxb., an herb known for its antihypertensive effect, lacks a comprehensive understanding of the mechanism underlying its antihypertensive action. This study aimed to elucidate the antihypertensive mechanism of aqueous extract of P. sarmentosum leaves (AEPS) via its modulation of the ACE pathway in phorbol 12-myristate-13-acetate (PMA)-induced human umbilical vein endothelial cells (HUVECs). HUVECs were divided into five groups: control, treatment with 200 µg/mL AEPS, induction 200 nM PMA, concomitant treatment with 200 nM PMA and 200 µg/mL AEPS, and treatment with 200 nM PMA and 0.06 μM captopril. Subsequently, ACE mRNA expression, protein level and activity, angiotensin II (Ang II) levels, and angiotensin II type 1 receptor (AT1R) and angiotensin II type 2 receptor (AT2R) mRNA expression in HUVECs were determined. AEPS successfully inhibited ACE mRNA expression, protein and activity, and angiotensin II levels in PMA-induced HUVECs. Additionally, AT1R expression was downregulated, whereas AT2R expression was upregulated. In conclusion, AEPS reduces the levels of ACE mRNA, protein and activity, Ang II, and AT1R expression in PMA-induced HUVECs. Thus, AEPS has the potential to be developed as an ACE inhibitor in the future.

PPARγ Agonist Rosiglitazone and Antagonist GW9662: Antihypertensive Effects on Chronic Intermittent Hypoxia-Induced Hypertension in Rats.

The increased incidence of hypertension associated with obstructive sleep apnea (OSA) presents significant physical, psychological, and economic challenges. Peroxisome proliferator-activated receptor gamma (PPARγ) plays a role in both OSA and hypertension, yet the therapeutic potential of PPARγ agonists and antagonists for OSA-related hypertension remains unexplored. Therefore, we constructed a chronic intermittent hypoxia (CIH)-induced hypertension rat model that mimics the pathogenesis of OSA-related hypertension in humans. The model involved administering PPARγ agonist rosiglitazone (RSG), PPARγ antagonist GW9662, or normal saline, followed by regular monitoring of blood pressure and thoracic aorta analysis using staining and electron microscopy. Intriguingly, our results indicated that both RSG and GW9662 appeared to potently counteract CIH-induced hypertension. In silico study suggested that GW9662's antihypertensive effect might mediated through angiotensin II receptor type 1 (AGTR1). Our findings provide insights into the mechanisms of OSA-related hypertension and propose novel therapeutic targets.

The central renin–angiotensin system: A genetic pathway, functional decoding, and selective target engagement characterization in humans

Accumulating evidence suggests that the brain renin angiotensin system (RAS) plays a pivotal role in the regulation of cognition and behavior as well as in the neuropathology of neurological and mental disorders. The angiotensin II type 1 receptor (AT1R) mediates most functional and neuropathology-relevant actions associated with the central RAS. However, an overarching comprehension to guide translation and utilize the therapeutic potential of the central RAS in humans is currently lacking. We conducted a comprehensive characterization of the RAS using an innovative combination of transcriptomic gene expression mapping, image-based behavioral decoding, and pre-registered randomized controlled discovery-replication pharmacological resting-state functional magnetic resonance imaging (fMRI) trials (N = 132) with a selective AT1R antagonist. The AT1R exhibited a particular dense expression in a subcortical network encompassing the thalamus, striatum, and amygdalo-hippocampal formation. Behavioral decoding of the AT1R gene expression brain map showed an association with memory, stress, reward, and motivational processes. Transient pharmacological blockade of the AT1R further decreased neural activity in subcortical systems characterized by a high AT1R expression, while increasing functional connectivity in the cortico-basal ganglia-thalamo-cortical circuitry. Effects of AT1R blockade on the network level were specifically associated with the transcriptomic signatures of the dopaminergic, opioid, acetylcholine, and corticotropin-releasing hormone signaling systems. The robustness of the results was supported in an independent pharmacological fMRI trial. These findings present a biologically informed comprehensive characterization of the central AT1R pathways and their functional relevance on the neural and behavioral level in humans.

Angiotensin II Type 2 Receptor Agonism Alleviates Progressive Post-stroke Cognitive Impairment in Aged Spontaneously Hypertensive Rats.

Hypertension and aging are leading risk factors for stroke and vascular contributions to cognitive impairment and dementia (VCID). Most animal models fail to capture the complex interplay between these pathophysiological processes. In the current study, we examined the development of cognitive impairment in 18-month-old spontaneously hypertensive rats (SHR) before and following ischemic stroke. Sixty SHRs were housed for 18months with cognitive assessments every 6months and post-surgery. MRI scans were performed at baseline and throughout the study. On day 3 post-stroke, rats were randomized to receive either angiotensin II type 2 receptor (AT2R) agonist Compound 21 (C21) or plain water for 8weeks. SHRs demonstrated a progressive cognitive decline and significant MRI abnormalities before stroke. Perioperative mortality within 72h of stroke was low. Stroke resulted in significant acute brain swelling, chronic brain atrophy, and sustained sensorimotor and behavioral deficits. There was no evidence of anhedonia at week 8. C21 enhanced sensorimotor recovery and ischemic lesion resolution at week 8. SHRs represent a clinically relevant animal model to study aging and stroke-associated VCID. This study underscores the importance of translational disease modeling and provides evidence that modulation of the AT2R signaling via C21 may be a useful therapeutic option to improve sensorimotor and cognitive outcomes even in aged animals.

Utilizing venous occlusion plethysmography to assess vascular effects: A study with buloxibutid, an angiotensin II type 2 receptor agonist.

Buloxibutid (also known as C21) is a potent and selective angiotensin II type 2 receptor (AT2R) agonist, in development for oral treatment of fibrotic lung disease. This phase I, open-label, pharmacodynamic study investigated vascular effects of buloxibutid in five healthy male volunteers. Subjects were administered intra-arterial infusions of buloxibutid for 5 min in ascending doses of 3, 10, 30, 100, and 200 μg/min, infused sequentially in the forearm. Infusions of sodium nitroprusside (SNP) solution in doses of 0.8-3.2 μg/min were administered as a positive control. Forearm blood flow (FBF) was measured by venous occlusion plethysmography. Safety and tolerability of intra-arterial administrations of buloxibutid were evaluated. Following infusion of buloxibutid in doses of 3-200 μg/min, the range of increase in FBF was 27.8%, 17.2%, 37.0%, 28.5%, and 60.5%, compared to the respective baseline. The largest increase was observed in the highest dose group. Infusions of SNP as a positive control, increased FBF 230-320% compared to baseline. Three adverse events (AEs) of mild intensity, not related to buloxibutid or SNP, were reported for two subjects. Two of these AEs were related to study procedures. There were no clinically relevant changes in arterial blood pressure during the study period. Intra-arterial infusion of buloxibutid in low, ascending doses increased FBF, indicating that buloxibutid may be effective in conditions associated with endothelial dysfunction. Venous occlusion plethysmography was found to be a useful method to explore pharmacodynamic vascular effects of novel AT2R agonists, while avoiding systemic adverse effects.

Asymmetric Phase-Transfer Alkylation of Readily Available Aryl Aldehyde Schiff Bases of Amino Acid Ethyl Esters.

Asymmetric phase-transfer alkylation of the N-(arylmethylene)-α-alkylamino acid ethyl esters and N-(arylmethylene)glycine ethyl esters was found to be catalyzed by the (R)- or (S)-Simplified Maruoka Catalyst with high efficiency and excellent enantioselectivity. This approach was successfully applied to the enantioselective formal synthesis of the angiotensin II type 2 receptor (AT2R) antagonists Olodanrigan and LX9211, and the practical aspect is demonstrated by the kilogram-scale synthesis of a key intermediate for the synthesis of LX9211.

Sparsentan is superior to losartan in the gddY mouse model of IgA nephropathy.

The mechanism leading to the development of IgA nephropathy (IgAN) remains to be completely understood. Endothelin-1 (ET-1) as well as angiotensin II (AngII) promote glomerular injury, tubulointerstitial inflammation, and fibrosis leading to chronic kidney disease. Sparsentan, a dual endothelin angiotensin receptor antagonist (DEARA), recently received accelerated approval in United States for the reduction of proteinuria in adults with IgAN at high risk of disease progression. To elucidate the mechanisms by which sparsentan is efficacious in IgAN, we examined the effect of treatment in gddY mice, a spontaneous IgAN mouse model, versus the monoselective angiotensin II type 1 receptor (AT1R) antagonist, losartan, on the development of renal injury at doses resulting in similar blood pressure lowering. Four-week-old gddY mice were given control chow, chow containing sparsentan, or drinking water containing losartan until 12 or 20 weeks old. Remarkably, the albumin:creatine ratio (ACR) was attenuated more rapidly and to a greater extent in mice treated with sparsentan than those treated with losartan. The decrease in ACR from baseline after 4 weeks of treatment correlated with beneficial effects of sparsentan on glomerulosclerosis and protection of podocytes and glycocalyx after 16 weeks of treatment across treatment groups; thus, sparsentan treatment delayed development of renal injury to a greater extent than losartan. Expression of mRNA for ET-1, ETAR, and AT1R and proinflammatory genes was upregulated in 12-week-old gddY mice and was prevented by sparsentan and losartan to a comparable extent. The results of this study, and in light of the results of the phase 3 PROTECT trial, provide a novel perspective and understanding of the mechanisms by which sparsentan has a beneficial renoprotective effect against IgAN compared to AT1R antagonism alone.

Renin-angiotensin system gene polymorphism and aging

A personalized healthy aging program, aimed at preservation of functional capacities in old ages, should consider genetic (hereditary) factors that determine the structure and functions of body organs and systems, and their age-related changes. Individual genetic characteristics of a person can influence the aging process. For this reason, recent research focuses on identifying genetic mechanisms of aging and longevity associated with multifactorial diseases. Renin-angiotensin system (RAS) contributes to the development of pathological conditions leading to cardiovascular diseases, cognitive changes, disorders of auditory and visual analyzers, and may determine the preservation of functional capacities in older adults. We present a literature review of the role of the RAS gene polymorphisms in the aging processes. The results of the synthesis of Russian and international literature indicated the contribution of polymorphic variants of the angiotensinogen (AGT), angiotensin-converting enzyme (ACE), and angiotensin II receptor type 1 (AGTR1) genes to the development of pathological conditions and the associated decreases in functional capacities of an elderly person. Testing for these polymorphisms can be of a practical importance for personified health assessment and development of timely preventive interventions aimed at improving life expectancy and quality of life among older adults.

Delayed Administration of an Angiotensin II Type 2 Receptor Agonist Promotes Functional Recovery of the Brain and Heart After Traumatic Brain Injury.

Cardiac injury is a common complication following traumatic brain injury (TBI) that can lead to poor clinical outcomes. Angiotensin II type 2 receptor (AT2R) activation exerts protective roles in the brain and heart, yet its potential impact on TBI or TBI-induced cardiac deficits remains elusive. The goal of this study was to investigate the influence of AT2R activation on recovery after TBI-induced cognitive and cardiac injury using the selective nonpeptide AT2R agonist compound 21 (C21). TBI was induced by cortical impact injury in male adult C57BL/6J mice, and the mice received C21 (0.03 mg/kg, intraperitoneally) starting from 24 h after TBI and continuing once daily. C21 facilitated cognitive function recovery until 1 month after TBI. C21 alleviated blood-brain barrier leakage and brain edema and inhibited the expression of proinflammatory cytokines in the brain after 3 consecutive days of treatment. C21 improved cerebral blood flow after 1 month, although the lesion volume was not affected. C21 also reduced the expression of proinflammatory cytokines in the heart after a 3-day consecutive treatment. Meanwhile, C21 benefited cardiac function, as identified by increased left ventricular ejection fraction 1 month after TBI. In addition, C21 alleviated TBI-induced cardiac hypertrophy and fibrosis; however, blood pressure was not affected. Our results demonstrate that AT2R activation ameliorates TBI-induced neurological and cardiac deficits.

AT1R autoantibody promotes phenotypic transition of smooth muscle cells by activating AT1R-OAS2

Phenotypic transition of vascular smooth muscle cells (VSMCs) is an early event in the onset and progression of several cardiovascular diseases. As an important mediator of the renin-angiotensin system (RAS), activation of the angiotensin II type 1 receptor (AT1R) induces phenotypic transition of VSMCs. AT1R autoantibodies (AT1-AAs), which are agonistic autoantibodies of AT1R, have been detected in the sera of patients with a variety of cardiovascular diseases associated with phenotypic transition. However, the effect of AT1-AA on phenotypic transition is currently unknown. In this study, AT1-AA-positive rat model was established by active immunization to detect markers of VSMCs phenotypic transition. The results showed that AT1-AA-positive rats showed phenotypic transition of VSMCs, which was evidenced by the decrease of contractile markers, while the increase of synthetic markers in the thoracic aorta. However, in AT1-AA-positive AT1R knockout rats, the phenotypic transition-related proteins were not altered. In vitro, after stimulating human aortic smooth muscle cells with AT1-AA for 48 h, 2′-5′ oligoadenylate synthase 2 (OAS2) was identified as the key differentially expressed gene by RNA sequencing and bioinformatics analysis. Furthermore, high expression of OAS2 was found in aorta of AT1-AA-positive rats; knockdown of OAS2 by siRNA can reverse the phenotypic transition of VSMCs induced by AT1-AA. In summary, this study suggests that AT1-AA can promote phenotypic transition of VSMCs through AT1R-OAS2 pathway, and OAS2 might serve as a potential therapeutic target to prevent pathological phenotypic transition of smooth muscle cells.

Angiotensin II-dependent aldosterone production in the adrenal cortex.

The adrenal cortex is responsible for production of adrenal steroid hormones and is anatomically divided into three distinct zones: zona glomerulosa secreting mineralocorticoids (mainly aldosterone), zona fasciculata secreting glucocorticoids (cortisol), and zona reticularis producing androgens. Importantly, due to their high lipophilicity, no adrenal steroid hormone (including aldosterone) is stored in vesicles but rather gets synthesized and secreted instantly upon cell stimulation with specific stimuli. Aldosterone is the most potent mineralocorticoid hormone produced from the adrenal cortex in response to either angiotensin II (AngII) or elevated K+ levels in the blood (hyperkalemia). AngII, being a peptide, cannot cross cell membranes and thus, uses two distinct G protein-coupled receptor (GPCR) types, AngII type 1 receptor (AT1R) and AT2R to exert its effects inside cells. In zona glomerulosa cells, AT1R activation by AngII results in aldosterone synthesis and secretion via two main pathways: (a) Gq/11 proteins that activate phospholipase C ultimately raising intracellular free calcium concentration; and (b) βarrestin1 and -2 (also known as Arrestin-2 and -3, respectively) that elicit sustained extracellular signal-regulated kinase (ERK) activation. Both pathways induce upregulation and acute activation of StAR (steroidogenic acute regulatory) protein, the enzyme that catalyzes the rate-limiting step in aldosterone biosynthesis. This chapter describes these two salient pathways underlying AT1R-induced aldosterone production in zona glomerulosa cells. We also highlight some pharmacologically important notions pertaining to the efficacy of the currently available AT1R antagonists, also known as angiotensin receptor blockers (ARBs) or sartans at suppressing both pathways, i.e., their inverse agonism efficacy at G proteins and βarrestins.