Angiotensin II Type 2 Receptor Agonist Research Articles

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.

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.

Gestational Intermittent Hypoxia Impairs AT2R-Mediated Vascular Protection in Female Offspring on a High-Fat, High-Sucrose Diet.

Gestational intermittent hypoxia (GIH), a hallmark of maternal obstructive sleep apnea, sex-differentially causes hypertension and endothelial dysfunction in adult male offspring but not in females. This study investigated whether the GIH-exposed female offspring, a "protected" group against the hypertensive effects of maternal GIH exposure, exhibit increased susceptibility to hypertension and cardiovascular dysfunction when fed a high-fat high-sucrose (HFHS) diet and whether this effect could be reversed by pharmacological intervention activating the angiotensin II type 2 receptor (AT2R). Female offspring of control and GIH-exposed (10.5% O2, 8 h/d, E10-21) dams were assigned either an HFHS diet or a standard diet from 12 weeks of age. Blood pressure was monitored. At 28 weeks, a systemic CGP42112 (AT2R agonist) or saline infusion was administered through the osmotic pump. At 30 weeks, the heart was weighed and collected for H&E staining, mesenteric arteries for vascular reactivity assessment and protein analysis, and plasma for ELISA. The HFHS diet induced similar increases in body weight gain and blood pressure in control and GIH female offspring. HFHS feeding did not affect heart structure, but impaired endothelial-dependent vascular relaxation with associated decreased AT2R and eNOS expression and reduced plasma bradykinin levels in both control and GIH offspring. CGP42112 administration effectively mitigated HFHS-induced hypertension and endothelial dysfunction only in control offspring, accompanied by restored AT2R, eNOS, and bradykinin levels, but not in the GIH counterparts. These findings suggest that GIH induces endothelial dysfunction and AT2R insensitivity in female offspring exposed to an HFHS diet.

Angiotensin-II type 2 receptor-mediated renoprotection is independent of receptor Mas in obese Zucker rats fed high-sodium diet.

The consumption of a high-sodium diet (HSD) is injurious and known to elevate blood pressure (BP), especially in obesity. Acute infusion studies depict a functional interdependency between angiotensin-II type 2 receptor (AT2R) and receptor Mas (MasR). Hence, we hypothesize that the subacute blockade of MasR should reverse AT2R-mediated renoprotection in obese Zucker rats (OZRs). Male OZRs were fed an HSD (for 14days) and treated with the AT2R agonist C21 (100ng/min) without or with a MasR antagonist A779 (1,000ng/min). The indices of oxidative stress, proteinuria, kidney injury, and BP were measured before and after, along with the terminal measurements of an array of inflammatory and kidney injury markers. The HSD significantly decreased the estimated glomerular filtration rate and urinary osmolality and increased thirst, diuresis, natriuresis, kaliuresis, plasma creatinine, urinary excretion of H2O2, proteinuria, renal expression and urinary excretion of kidney injury markers (NGAL and KIM-1), and BP indexes. The HSD feeding showed early changes in the renal expression of CRP, ICAM-1, and galectin-1. The C21 treatment prevented these pathological changes. The MasR antagonist A779 attenuated C21-mediated effects on the urinary excretion and renal expression of NGAL and oxidative stress in the absence of inflammation and BP changes. Overall, we conclude that the subacute functional interactions between AT2R and MasR are weak or transient and that the beneficial effects of AT2R activation are independent of the MasR blockade in the kidney of male obese rats fed an HSD.

Acute In Vivo Administration of Compound 21 Stimulates Akt and ERK1/2 Phosphorylation in Mouse Heart and Adipose Tissue

The angiotensin II type 2 (AT2) receptor has a role in promoting insulin sensitivity. However, the mechanisms underlying the AT2 receptor-induced facilitation of insulin are still not completely understood. Therefore, we investigated whether acute in vivo administration of AT2 receptor agonist compound 21 (C21) could activate insulin signaling molecules in insulin-target tissues. We report that, in male C57BL/6 mice, an acute (5 min, 0.25 mg/kg; i.v.) injection of C21 induces the phosphorylation of Akt and ERK1/2 at activating residues (Ser473 and Thr202/Tyr204, respectively) in both epididymal white adipose tissue (WAT) and heart tissue. In WAT, the extent of phosphorylation (p) of Akt and ERK1/2 induced by C21 was approximately 65% of the level detected after a bolus injection of a dose of insulin known to induce maximal activation of the insulin receptor (IR). In the heart, C21 stimulated p-Akt to a lesser extent than in WAT and stimulated p-ERK1/2 to similar levels to those attained by insulin administration. C21 did not modify p-IR levels in either tissue. We conclude that in vivo injection of the AT2 receptor agonist C21 activates Akt and ERK1/2 through a mechanism that does not involve the IR, indicating the participation of these enzymes in AT2R-mediated signaling.

Novel AT2R agonist, β-Pro7Ang III, is cardio- and vaso-protective in diabetic spontaneously hypertensive rats

Stimulation of the angiotensin II type 2 receptor (AT2R) evokes protective effects in various cardiovascular diseases. Thus, this study aimed to investigate the effects of AT2R stimulation, with or without AT1R blockade, in a model of hypertension with concomitant type 1 diabetes mellitus (T1DM). Spontaneously hypertensive rats (SHRs) were given either citrate or a single dose of streptozotocin (STZ; 55 mg/kg, i.p.) to induce diabetes. After 4 weeks of diabetes, animals were administered either a vehicle (saline), AT2R agonist, β-Pro7Ang III (0.1 mg/kg/day via osmotic mini-pump), AT1R blocker, candesartan (2 mg/kg/day via drinking water), or a combination of both for a further 8 weeks. β-Pro7Ang III treatment had no effect on blood pressure, but attenuated the significant increase in cardiac interstitial collagen and protein expression of fibrotic and inflammatory markers, and superoxide levels that was evident in diabetic SHRs. These effects were not observed with candesartan, despite its blood pressure lowering effects. Although β-Pro7Ang III had no effect on aortic fibrosis, it significantly attenuated MCP-1 protein expression and superoxide levels when compared to both the non-diabetic and diabetic SHRs, to a similar extent as candesartan. In both the heart and vasculature, the effects of β-Pro7Ang III in combination with candesartan were similar to those of β-Pro7Ang III alone, and superior to candesartan alone. It was concluded that in hypertension with concomitant diabetes, AT2R stimulation with a novel ligand alone, or in combination with AT1R blockade, improved the cardiac and vascular structural changes that were strongly associated with inflammation and oxidative stress, independent of blood pressure regulation.

Angiotensin II type 2 receptor agonist attenuates LPS-induced acute lung injury through modulating THP-1-derived macrophage reprogramming.

Acute respiratory distress syndrome (ARDS) is a devastating respiratory disorder, characterized by overwhelming inflammation in the alveoli without effective pharmacological treatment. We aimed to investigate the effect and mechanism of angiotensin II type 2 receptor (AT2R) agonist, Compound 21 (C21), on the lipopolysaccharide (LPS)-induced acute lung injury (ALI) model. The protective effect of C21 was evaluated via enzyme-linked immunosorbent assay (ELISA), Western blot (WB), real-time PCR, and fluorescence microscopy in LPS-challenged THP1-derived macrophages. Besides, the in vivo efficacy of C21 was assessed using cell counting, ELISA, protein quantification, hematoxylin-eosin (H&E) staining, and WB in an LPS-induced ALI mouse model. The results showed thatC21 significantly inhibited the secretion of pro-inflammatory cytokines (CCL-2, IL-6), overproduction of intracellular ROS, and activation of inflammatory pathways (NF-κB/NLRP3, p38/MAPK) in THP-1 cell-derived macrophages stimulated by LPS. In in vivo study, intraperitoneal injection of C21 could reduce airway leukocytes accumulation and chemokine/cytokine (keratinocyte chemoattractant (KC), IL-6) generation, as well as alleviate diffuse alveolar damage induced by LPS. Conclusively,the AT2R agonist C21 significantly inhibited LPS-stimulated excess inflammatory responses and oxidative stress in macrophages. Meanwhile, C21 could effectively alleviate acute inflammation and tissue damage in the lungs of ALI mice challenged by LPS. The results of this study bring new hope for the early treatment of ALI/ARDS.

Angiotensin II type 2 receptor as a novel activator of brown adipose tissue in obesity.

The angiotensin II type 2 receptor (AT2R) exerts vasorelaxant, anti-inflammatory, and antioxidant properties. In obesity, its activation counterbalances the adverse cardiovascular effects of angiotensin II mediated by the AT1R. Preliminary results indicate that it also promotes brown adipocyte differentiation in vitro. Our hypothesis is that AT2R activation could increase BAT mass and activity in obesity. Five-week-old male C57BL/6J mice were fed a standard or a high-fat (HF) diet for 6 weeks. Half of the animals were treated with compound 21 (C21), a selective AT2R agonist, (1 mg/kg/day) in the drinking water. Electron transport chain (ETC), oxidative phosphorylation, and UCP1 proteins were measured in the interscapular BAT (iBAT) and thoracic perivascular adipose tissue (tPVAT) as well as inflammatory and oxidative parameters. Differentiation and oxygen consumption rate (OCR) in the presence of C21 was tested in brown preadipocytes. In vitro, C21-differentiated brown adipocytes showed an AT2R-dependent increase of differentiation markers (Ucp1, Cidea, Pparg) and increased basal and H+ leak-linked OCR. In vivo, HF-C21 mice showed increased iBAT mass compared to HF animals. Both their iBAT and tPVAT showed higher protein levels of the ETC protein complexes and UCP1, together with a reduction of inflammatory and oxidative markers. The activation of the AT2R increases BAT mass, mitochondrial activity, and reduces markers of tissue inflammation and oxidative stress in obesity. Therefore, insulin reduction and better vascular responses are achieved. Thus, the activation of the protective arm of the renin-angiotensin system arises as a promising tool in the treatment of obesity.

Effects of the Oral Angiotensin II Type 2 Receptor Agonist C21 in Sugen-Hypoxia Induced Pulmonary Hypertension in Rats.

Substantial evidence supports the involvement of the renin-angiotensin system in pulmonary hypertension (PH), and the angiotensin II type 2 receptor (AT2R) is known to exert tissue protective actions. The effect of the selective AT2R agonist C21 (also known as Compound 21 or buloxibutid) was evaluated in the rat Sugen-hypoxia PH model. After a single injection of Sugen 5416 and hypoxia for 21 days, C21 (2 or 20 mg/kg) or vehicle was administered perorally twice daily from Day 21 to Day 55. On Day 56, hemodynamic assessments were performed, and lung and heart tissue were prepared for quantification of cardiac and vascular remodeling and fibrosis. Treatment with C21 20 mg/kg improved cardiac output and stroke volume and decreased right ventricular hypertrophy (all p < 0.05). Treatment with C21 2 mg/kg significantly decreased vessel wall and muscular layer thickness and increased the luminal opening in vessels >100 μm (all p < 0.05). There were no significant differences between the two C21 doses on any parameter, and post hoc analyses comparing the merged C21 groups with the vehicle group showed that C21 treatment reduced vascular remodeling (reduced endothelial proliferation and thickening of the vascular wall) in vessels of all sizes; moreover, the diastolic pulmonary artery pressure and right ventricular pressure were reduced along with reduction of right ventricular hypertrophy. Sugen 5416 and hypoxia increased pulmonary collagen deposition, which was counteracted by C21 20 mg/kg. In conclusion, the effects of C21 on vascular remodeling, hemodynamic alterations, and fibrosis suggest that AT2R agonists may have a role in Group 1 and 3 PH treatment.

Angiotensin II type 2 receptor activation preserves megalin in the kidney and prevents proteinuria in high salt diet fed rats

Proteinuria is a risk factor for and consequence of kidney injury. Angiotensin II type 2 receptor (AT2R) is an emerging reno-protective target and is anti-proteinuric under pathological conditions, including high salt-fed obese animals. However, the mechanisms remain unknown, particularly whether the anti-proteinuric activity of AT2R is independent of its anti-hypertensive and anti-inflammatory effects. In the present study, obese Zucker rats were fed high sodium (4%) diet (HSD) for 48 h, a time in which blood pressure does not change. HSD caused proteinuria without affecting glomerular slit diaphragm proteins (nephrin and podocin), glomerular filtration rate, inflammatory and fibrotic markers (TNFα, IL-6, and TGF-β), ruling out glomerular injury, inflammation and fibrosis but indicating tubular mechanisms of proteinuria. At cellular and molecular levels, we observed a glycogen synthase kinase (GSK)-3β-mediated megalin phosphorylation, and its subsequent endocytosis and lysosomal degradation in HSD-fed rat kidneys. Megalin is a major proximal tubular endocytic protein transporter. The AT2R agonist C21 (0.3 mg/kg/day, i.p.) administration prevented proteinuria and rescued megalin surface expression potentially by activating Akt-mediated phosphorylation and inactivation of GSK-3β in HSD-fed rat kidneys. Overall, AT2R has a direct anti-proteinuric activity, potentially via megalin regulation, and is suggested as a novel target to limit kidney injury.

Investigation of the effect of the angiotensin II type 2 receptor (AT2R) agonist C21 on plasma NT-proBNP, a diagnostic biomarker, in subjects hospitalised with COVID-19

Abstract The prohormone N-terminal pro-B-type natriuretic peptide (NT-proBNP) is released from stretched cardiac myocytes and is a diagnostic biomarker for heart failure and cardiac dysfunction as well as pulmonary embolism and pneumonia that are frequent complications to severe Coronavirus Disease 2019 (COVID-19). NT-proBNP is frequently elevated in COVID-19. In a recent publication, it was demonstrated that NT-proBNP was strongly associated with mortality in patients with COVID-19, and further investigation of its usefulness as a prognostic tool to predict disease outcomes in COVID-19 was suggested (1). In the recently completed phase 2 trial (angiotensin II type 2 receptor agonist COVID-19 trial [ATTRACT]; NCT04452435) in subjects hospitalised with COVID-19, it was investigated whether treatment with the AT2R agonist C21 for 7 days affected the release of the plasma biomarker NT-proBNP. ATTRACT was a randomised, double-blind, placebo-controlled, phase 2 trial that investigated the safety and efficacy of C21 treatment (100 mg twice daily) for 7 days in hospitalised subjects with COVID-19, not requiring mechanical ventilation. The results of the trial demonstrated that treatment with C21 on top of standard of care (vast majority of patients received glucocorticoids) significantly reduced the proportion of subjects requiring supplemental oxygen at Day 14, indicating faster recovery with C21 treatment compared to placebo. Blood samples for exploratory analysis were taken before and after 7 days of treatment with C21 or placebo. Plasma NT-proBNP was markedly elevated in both treatment groups before treatment, with average values of 357 and 438 pg/mL in the placebo and C21 groups, respectively, as compared to normal levels of approximately &amp;lt;100 pg/mL. After 7 days of treatment, the C21 group experienced a dramatic reduction in plasma NT-proBNP (by 259 pg/mL) as compared to the placebo group (63 pg/mL) (p=0.02). The results show that short-term C21 treatment decreased the release of NT-proBNP in subjects hospitalised with COVID-19. Further investigations are needed to elucidate whether this is related to effects on COVID-19-induced pulmonary damage or direct protective effects on the heart. We are currently conducting a global phase 3 trial (VP-C21–008) further investigating the effect of C21 in subjects hospitalised with COVID-19 including determination of NT-proBNP. Funding Acknowledgement Type of funding sources: Private company. Main funding source(s): Vicore Pharma AB

Angiotensin II type-2 receptor activation in alveolar macrophages mediates protection against cigarette smoke-induced chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is the third leading cause of death globally. Cumulative evidence has implicated renin-angiotensin system (RAS) in the pathogenesis of COPD. Alveolar macrophages (AMs) are the first line immune defense in the respiratory system and play a critical role in the lung homeostasis. This study aimed to investigate the role of AMs in contributing to the protective effects of angiotensin II type-2 receptor (AT2R) activation in cigarette smoke (CS)-induced COPD. The AM polarization, phagocytosis and metabolism, and the underlying biochemical mechanisms of compound 21 (C21), a selective and potent non-peptide small molecule AT2R agonist, were evaluated in a two-week CS-induced COPD mouse model. C21 restored AM phagocytosis ability, reversing CS-induced AM phagocytosis impairment. CS exposure polarized AMs towards M1 phenotype, whereas, C21 skewed the CS-exposed AMs towards M2 phenotype. C21 reprogrammed CS-exposed AM metabolism from a high glycolysis-driven process to support inflammation energy demand to a high mitochondrial respiration process to limit inflammation. Besides, C21 upregulated AT2R and Mas receptor levels in CS-exposed AMs, favoring the anti-inflammatory Ang II/AT2R axis and Ang 1–7/Mas axis in the RAS. C21 restored the normal levels of sirtuin 1 (SIRT1) and MAPK phosphatase 1 (MKP1) in CS-exposed AMs, leading to the reduction of phospho-p38, phospho-ERK and p65 subunit of NF-κB levels in CS-exposed AMs. We report here for the first time that AT2R agonist C21 acts by boosting the protective functions of AMs against CS-induced COPD, and our results support the development of AT2R agonist for the treatment of COPD.

Angiotensin II type-2-receptor stimulation ameliorates focal and segmental glomerulosclerosis in mice.

Podocyte damage and loss are the early event in the development of focal segmental glomerulosclerosis (FSGS). Podocytes express angiotensin II type-2-receptor (AT2R), which may play a key role in maintaining kidney integrity and function. Here, we examined the effects of AT2R deletion and AT2R agonist compound 21 (C21) on the evolution of FSGS. FSGS was induced by adriamycin (ADR) injection in both male wild-type (WT) and AT2R knockout (KO) mice. C21 was administered to WT-FSGS mice either one day before or 7 days after ADR (Pre-C21 or Post-C21), using two doses of C21 at either 0.3 (low dose, LD) or 1.0 (high dose, HD) mg/kg/day. ADR-induced FSGS was more severe in AT2RKO mice compared with WT-FSGS mice, and included profound podocyte loss, glomerular fibrosis, and albuminuria. Glomerular cathepsin L expression increased more in AT2RKO-FSGS than in WT-FSGS mice. C21 treatment ameliorated podocyte injury, most significantly in the Pre C21-HD group, and inhibited glomerular cathepsin L expression. In vitro, Agtr2 knock-down in mouse podocyte cell line given ADR confirmed the in vivo data. Mechanistically, C21 inhibited cathepsin L expression, which protected synaptopodin from destruction and stabilized actin cytoskeleton. C21 also prevented podocyte apoptosis. In conclusion, AT2R activation by C21 ameliorated ADR-induced podocyte injury in mice by the inhibition of glomerular cathepsin L leading to the maintenance of podocyte integrity and prevention of podocyte apoptosis.

Sexually dimorphic role of smooth muscle cell estrogen receptor alpha in aging‐associated arterial stiffness

BackgroundAging is associated with rising arterial stiffness (AS), an independent risk factor for cardiovascular disease. The development of aging‐associated AS follows a sexually dimorphic pattern with women developing AS later in life. Estrogen and estrogen receptor alpha (ERα) are protective in the premenopausal state, potentially due to the regulation of the vasoprotective angiotensin II type 2 receptor (AT2R), however, the role of estrogen/ERα in aging‐associated AS has not been defined and the mechanisms of the sexually‐dimorphic development of aging‐associated AS are unknown.Methods/ResultsAll studies were conducted in accordance with the FASEB Statement of Principles for the use of Animals in Research and Education. We generated novel smooth muscle cell‐specific ERα‐KO mice and measured aortic pulse wave velocity (PWV), an index of AS, in 3, 12, and 18 month old male and female intact and KO mice. Male mice develop increases in AS from 3 to 12 months compared to 3 to 18 months in females (p&lt;0.05). SMC‐ERα‐KO protected females from the aging‐associated increase in AS (p&lt;0.05). Circulating estrogens also declined in 18 month old females vs. 3 mo. (p&lt;0.05), suggesting a role for unliganded SMC‐ERα in aging‐associated AS. SMC‐ERα‐KO females were also protected from the aging‐associated decline in aortic AT2R expression observed in intact females (p&lt;0.05). To further investigate the potential role of unliganded SMC‐ERα in AS, we performed ovariectomy (OVX) or sham surgeries in young female SMC‐ERα‐Intact and KO mice and measured PWV. Results demonstrated an OVX‐driven increase in AS that was prevented by SMC‐ERα‐KO (p&lt;0.05). This was also associated with an OVX‐mediated decrease in aortic expression of the AT2R, which was prevented by SMC‐ERα‐KO. To determine the in vivo role of AT2R in the vascular protection observed in 12 month old female mice, we treated 12 month old male and female mice with AT2R antagonist PD‐123319 (3mg/kg/day) or vehicle via osmotic minipumps for 4 weeks. Chronic inhibition of the AT2R increased AS in 12 month old females (p&lt;0.05), but not males, suggesting that AT2R‐mediated protection contributes to the delay in aging‐associated AS in female mice. In vitro studies also demonstrated that estrogen upregulates AT2R mRNA and protein in female mouse aortic SMC, supporting an estrogen‐mediated mechanism of AT2R driven vascular protection in females.ConclusionThese data indicate sex differences in the time course of the development of aging‐associated arterial stiffness and suggest the presence of unliganded SMC‐ERα contributes specifically to aging‐associated arterial stiffness in females via reductions in vascular AT2R. Further, these results implicate that AT2R agonist therapy may improve cardiovascular outcomes in aging women to retain the beneficial downstream effects of estrogen signaling, without the potential detrimental effects of hormone replacement therapy.

Anti-Hypertensive Potential and Epigenetics of Angiotensin II type 2 Receptor (AT2R).

Renin angiotensin system (RAS) is a critical pathway involved in blood pressure regulation. Octapeptide, angiotensin II (Ang II), is a biologically active compound of RAS pathway which mediates its action by binding to either angiotensin II type 1 receptor (AT1R) or angiotensin II type 2 receptor (AT2R). Binding of Ang II to AT1R facilitates blood pressure regulation, whereas AT2R is primarily involved in wound healing and tissue remodeling. Recent studies have highlighted the additional role of AT2R to counterbalance the detrimental effects of AT1R. Activation of angiotensin II type 2 receptor using AT2R agonist has shown the effect on natriuresis and release of nitric oxide. Additionally, AT2R activation has been found to inhibit angiotensin converting enzyme (ACE) and enhance angiotensin receptor blocker (ARB) activity. These findings highlight the potential of AT2R as a novel therapeutic target against hypertension. The potential role of AT2R highlights the importance of exploring additional mechanisms that might be crucial for AT2R expression. Epigenetic mechanisms, including DNA methylation and histone modification, have been explored vastly with relation to cancer, but the role of such mechanisms in the expression of AT2R has recently gained interest.

Angiotensin II type 2 receptor agonist, compound 21, prevents tubular epithelial cell damage caused by renal ischemia

During ischemic acute kidney injury (AKI), loss of cytoskeletal integrity and disruption of intercellular junctions are rapid events in response to ATP depletion. Angiotensin II type 2 receptor (AT2R) is overexpressed in injury situations and its stimulation by angiotensin II (AngII) is related to beneficial renal effects. Its role on ischemic AKI has not been deeply studied. The aim of the present study was to investigate whether pretreatment with the AT2R agonist, C21, prevents ischemic renal epithelial cell injury. Studies in a model of 40 min of renal ischemia followed by 24 h of reperfusion (IR) in rats demonstrated that C21 pretreatment attenuated renal dysfunction and induced better preservation of tubular architecture. In addition, we studied the expression of Rho GTPases, RhoA and Cdc42, since they are key proteins in the regulation of the actin cytoskeleton and the stability of epithelial intercellular junctions. IR downregulated RhoA and Cdc42 abundance in rat kidneys. C21 pretreatment prevented RhoA reduction and increased Cdc42 abundance compared to controls. We also used an in vitro model of ATP depletion in MDCK cells grown on filter support. Using immunofluorescence we observed that in MDCK cells, C21 pretreatment prevented the ATP depletion-induced reduction of actin in brush border microvilli and in stress fibers. Moreover, C21 prevented membrane E-cadherin reduction, and RhoA and Cdc42 downregulation. The present study describes for the first time a renoprotective effect of the AT2R agonist, C21, against AKI, and provides evidence supporting that stimulation of AT2R triggers cytoprotective mechanisms against an ischemic event.

Facilitation of TRKB Activation by the Angiotensin II Receptor Type-2 (AT2R) Agonist C21.

Blockers of angiotensin II type 1 receptor (AT1R) exert antidepressant-like effects by indirectly facilitating the activation of the angiotensin II type 2 receptor (AT2R), which leads to increased surface expression and transactivation of tropomyosin-related kinase B receptors (TRKB). Compound 21 (C21) is a non-peptide AT2R agonist that produces neuroprotective effects. However, the behavioral effects of C21 and its involvement with the brain-derived neurotrophic factor (BDNF)-TRKB system still need further investigation. The aim of the present study was to assess the effect of C21 on the activation of TRKB and its consequences on conditioned fear. The administration of C21 (0.1–10 μM/15 min) increased the surface levels of TRKB but was not sufficient to increase the levels of phosphorylated TRKB (pTRKB) in cultured cortical neurons from rat embryos. Consistent with increased TRKB surface expression, C21 (10 μM/15 min or 3 days) facilitated the effect of BDNF (0.1 ng/mL/15 min) on pTRKB in these cells. In contextual fear conditioning, the freezing time of C21-treated (administered intranasally) wild-type mice was decreased compared to the vehicle-treated group, but no effect of C21 was observed in BDNF.het animals. We observed no effect of C21 in the elevated plus-maze test for anxiety. Taken together, our results indicate that C21 facilitated BDNF effect by increasing the levels of TRKB on the cell surface and reduced the freezing time of mice in a BDNF-dependent manner, but not through a general anxiolytic-like effect.

Activation of angiotensin II type‐2 receptor protects against cigarette smoke‐induced COPD

Chronic obstructive pulmonary disease (COPD) is the third leading cause of death globally. Cumulative evidence has implicated renin-angiotensin system (RAS) in the pathogenesis of COPD. This study aimed to investigate potential protective effects of angiotensin II type-2 receptor (AT2R) activation in cigarette smoke (CS)-induced COPD models and alveolar macrophages. Compound 21 (C21), a selective and potent non-peptide small molecule AT2R agonist, was evaluated for anti-inflammatory, anti-oxidative and anti-remodeling activities in a two-week (acute) and an eight-week (chronic) CS-induced COPD models. C21 inhibited CS-induced increases in macrophage and neutrophil counts, pro-inflammatory cytokines and oxidative damage markers in bronchoalveolar lavage (BAL) fluid, and TGF-β1 in lung tissues, from COPD models. C21 restored phosphatase activities and reduced phospho-p38 MAPK, phospho-ERK and p65 subunit of NF-κB levels in CS-exposed lung tissues. C21 also suppressed CS-induced increases in α-Sma, Mmp9, Mmp12and hydroxyproline levels in lung tissues, and neutrophil elastase activity in BAL fluid. C21 modulated RAS in CS-exposed lungs by downregulating Ang II but upregulating Ang-(1-7) and Mas receptor levels. C21 prevented CS-induced emphysema and improved lung functions in chronic COPD model. In conclusion, AT2R agonist C21 facilitates protective effects against CS-induced COPD, and provide strong evidence for further exploration of AT2R agonist effects on CS-induced alveolar macrophages.

Combination of AT2R Agonist and Neprilysin Inhibitor is Superior Than the Combination of AT1R Antagonist and Neprilysin Inhibitor in Protecting Kidney from Injury in High‐Salt Fed Obese Rats

Angiotensin II type 1 receptor (AT1R) antagonists, angiotensin II type 2 receptor (AT2R) agonists, and atrial natriuretic peptide (ANP) are natriuretics that provide reno- and cardiovascular protection and reduce blood pressure and volume load. An approved combination therapy (Entresto) of the AT1R blocker valsartan (VAL), and inhibitor of the ANP degrading enzyme neprilysin (NEP) sacubitril (SAC), for patients with heart failure and reduced ejection fraction was found to be associated with increased albuminuria, an indicator of kidney injury. Based on studies showing that AT2R activation affects various renin angiotensin system (RAS) components by decreasing activity of the classical arm components, and increasing expression and activity of those of the protective arm such as angiotensin converting enzyme 2 (ACE2), we hypothesized that AT2R agonist treatment in combination with SAC will provide better reno-protection compared to VAL + SAC. We tested this hypothesis in obese Zucker rats (OZR), in which kidney injury was induced by feeding a high salt diet. Male OZR were fed a 0.4% normal sodium (NSD) or 4% high sodium diet (HSD) and administered vehicle, AT2R agonist C21 (1 mg/kg/day) + SAC (10 mg/kg/day), or VAL (10 mg/kg/day) + SAC (10 mg/kg/day) (16 days, daily gavage). While total food intake was significantly decreased and water intake significantly increased by HSD feeding, neither treatment had an effect compared to the control group. Yet, C21 + SAC treatment, not VAL + SAC, prevented increases in body weight gain and kidney weight, a sign of hypertrophy. Analysis of 24-hr urine samples revealed that HSD caused a marked increase in albuminuria and proteinuria, which was significantly prevented by only C21 + SAC treatment. ANP was similarly preserved and associated with comparable inhibition of NEP activity in both treatment groups compared to HSD control. Furthermore, C21 + SAC treatment caused an increase in the renal expression of ACE2, and a decrease in renal renin activity, unlike VAL + SAC treatment. Moreover, HSD caused a reduction in plasma renin levels, which were increased 3-times by VAL + SAC, but not by C21 + SAC. Renal AT2R expression was unchanged in all treatment groups compared with HSD control group. On the other hand, renal AT1R expression was modestly increased by only VAL + SAC treatment. Taken together, this data suggests the combination of C21 + SAC provides strong reno-protection in obese animals fed HSD and is superior to the protection afforded by the combination of VAL + SAC. Differential regulation of the opposing arms of the RAS may be the basis of the superiority of C21 + SAC over VAL + SAC.

Angiotensin‐II type 2 receptor activation modulates renal neprilysin and coronavirus receptor angiotensin converting enzyme‐2 expression and activity in obese rats fed high salt diet

Neprilysin and coronavirus receptor angiotensin‐converting enzyme‐2 (ACE2) are peptidases critically involved in the breakdown of deleterious angiotensin‐II and the formation of protective angiotensin‐(1‐7). A disintegrin and metalloproteinase‐17 (ADAM17) is involved in the shedding of neprilysin and ACE2. We have reported the increase in renal angiotensin‐(1‐7) formation upon activation of angiotensin‐II type 2 receptor (AT2R). However, the modulation of expression and activity of these peptidases upon stimulation of AT2R in the kidney under the normal, obese, and high‐salt diet (HSD)‐fed condition is not known. Hence, we have treated, male, lean and obese Zucker rats (OZR) for 14 days without or with AT2R agonist C21 (1 mg/kg/day, via osmotic pumps) while fed HSD or normal diet. We have observed that the activity of neprilysin and ACE2 is decreased in the kidney of OZR fed either diet, however, only neprilysin activity has been found increased in the plasma (p<0.05). The C21‐treatment increased renal neprilysin expression and activity in the HSD‐fed OZR reflecting an increase in the urinary but decreased plasma activity (p<0.05). Likewise, The renal ACE2 expression is also increased upon C21‐treatment in HSD‐fed OZR and lean rats (p<0.05), but not the activity. These changes may be ascribed to ADAM17, as the renal expression of ADAM17 is paradoxically decreased upon HSD feeding in OZR (p<0.05) which is further reduced by C21‐treatment. Results indicate that AT2R activation differentially affects renal neprilysin and ACE2 which is critical in reference to current coronavirus pandemic.