Prevention of lipopolysaccharide-induced CD11b+ immune cell infiltration in the kidney: role of AT2 receptors

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 14 days) and treated with the AT2R agonist C21 (100 ng/min) without or with a MasR antagonist A779 (1,000 ng/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.

The gut-brain and gut-macrophage contribution to gastrointestinal dysfunction with systemic inflammation

The gastrointestinal tract is one of the main organs affected during systemic inflammation and disrupted gastrointestinal motility is a major clinical manifestation. Many studies have investigated the involvement of neuroimmune interactions in regulating colonic motility during localized colonic inflammation, i.e., colitis. However, little is known about how the enteric nervous system and intestinal macrophages contribute to dysregulated motility during systemic inflammation. Given that systemic inflammation commonly results from the innate immune response against bacterial infection, we mimicked bacterial infection by administering lipopolysaccharide (LPS) to rats and assessed colonic motility using ex vivo video imaging techniques. We utilized the Cx3cr1-Dtr rat model of transient depletion of macrophages to investigate the role of intestinal macrophages in regulating colonic motility during LPS infection. To investigate the role of inhibitory enteric neurotransmission on colonic motility following LPS, we applied the nitric oxide synthase inhibitor, Nω-nitro-L-arginine (NOLA). Our results confirmed an increase in colonic contraction frequency during LPS-induced systemic inflammation. However, neither the depletion of intestinal macrophages, nor the suppression of inhibitory enteric nervous system activity impacted colonic motility disruption during inflammation. This implies that the interplay between the enteric nervous system and intestinal macrophages is nuanced, and complex, and further investigation is needed to clarify their joint roles in colonic motility.

Telmisartan ameliorates nephropathy and restores the hippo pathway in rats with metabolic syndrome

The main objective of this study was to determine if the telmisartan-ameliorative effects of metabolic syndrome (MetS)-evoked nephropathy are attributed to the Hippo pathway. A secondary objective was to investigate the potential of vitamin D3 to enhance telmisartan-favourable effects. A diet composed of 24% fat and 3% salt, along with drinking water containing 10% fructose, was administered for 12 weeks to induce MetS. MetS-rats were given telmisartan (5 mg/kg/day), vitamin D3 (10 μg/kg/day) or both by gavage, starting in the sixth week of experimental diet administration. Assessments performed at closure included renal function, histological examination, catalase, malondialdehyde (MDA), nuclear factor kappa-B (NF-κB), interleukin-6 (IL-6), peroxisome proliferator-activated receptor-γ (PPAR-γ), phosphatase and tensin homolog (PTEN), and transforming growth factor-β (TGF-β). Matrix metalloproteinase-9 (MMP-9) immunostaining was conducted. The expression of the Hippo pathway components, as well as that of angiotensin II type 1 and type 2 (AT1 and AT2), receptors was evaluated. Telmisartan attenuated MetS-evoked nephropathy, as demonstrated by improvement of renal function and histological features, enhancement of catalase, reduction of MDA, inflammation (NF-κB, IL-6), and renal fibrosis (increased PPAR-γ and PTEN and reduced MMP-9 and TGF-β). Telmisartan downregulated AT1-receptor, upregulated AT2-receptor and restored the Hippo pathway. Vitamin D3 replicated most of the telmisartan-elicited effects and enhanced the antifibrotic actions of telmisartan. The alleviative effects of telmisartan on MetS-evoked nephropathy may be related to the restoration of the Hippo pathway. The combination of vitamin D3 and telmisartan exerted more favourable effects on metabolic and nephropathic biomarkers compared with either one administered alone.

Angiotensin II Type 2 Receptor Antibodies in Glomerular Diseases

We evaluated the concentration of AT2R antibodies in 136 patients with primary and secondary glomerular diseases: membranous nephropathy (n = 18), focal and segmental glomerulosclerosis (n = 25), systemic lupus erythematosus (n = 17), immunoglobulin A (IgA) nephropathy (n = 14), mesangial (non-IgA) proliferative nephropathy (n = 6), c-ANCA vasculitis (n = 40), perinuclear anti-neutrophil cytoplasmic antibodies (p-ANCA) vasculitis (n = 16), and compared it with a healthy control group (22 patients). Serum creatinine levels, proteinuria, serum albumin, and total protein concentrations were prospectively recorded for 2 years. The mean levels of AT2R antibodies in the lupus nephropathy group were significantly higher compared to the control group, 64.12 ± 26.95 units/mL and 9.72 ± 11.88 units/mL, respectively. There was no association between this level and the clinical course of the disease. The AT2R levels in other kinds of glomerular disease were no different from the control group. We found significant correlations between AT1R and AT2R in patients with membranous nephropathy (r = 0.66), IgA nephropathy (r = 0.61), and c-ANCA vasculitis (r = 0.63). Levels of AT2R antibodies in systemic lupus erythematosus are higher compared to other types of glomerulonephritis, vasculitis, and a healthy control group. Levels of AT2R antibodies correlate with AT1R antibodies in the groups of patients with membranous nephropathy, IgA nephropathy, and c-ANCA vasculitis. These kinds of AT2R antibodies have a stimulative effect on AT2R, but we have not found the influence of these antibodies on the clinical course of glomerular diseases.

Macrophage angiotensin AT2 receptor activation is protective against early phases of LPS-induced acute kidney injury

Lipopolysaccharide (LPS)-induced acute kidney injury (AKI) is characterized by inflammation and infiltration of immune cells, mainly neutrophils and macrophages, and results in sudden renal dysfunction. Previously, we have reported the anti-inflammatory and renoprotective role of the angiotensin II type 2 receptor (AT2R), expressed on kidney tubular cells and immune cells, in LPS-induced AKI. Moreover, in vitro studies revealed macrophage AT2R activation shifts the cells to the anti-inflammatory M2 subtype. However, the protective role of the macrophage AT2R in a model of AKI is unknown. The present study addressed this question by adoptive transfer of bone marrow-derived macrophages (BMDMs) in systemic macrophage-depleted mice. We acquired significant systemic macrophage depletion by two doses of liposomal clodronate (CLD), and the mice were repopulated with BMDMs (CD11b+F4/80+, double positive) primed with AT2R agonist C21 (CLD + MacC21 + LPS) or vehicle (CLD + Mac + LPS) in vitro for 60 min, followed by LPS (5 mg/kg body wt ip) challenge. We observed a gradual increase in the CD11b+ cells at 2 and 24 h after the LPS challenge. However, kidney CD11b+ cells in the CLD + Mac + LPS group were elevated compared with the CLD + MacC21 + LPS group at 2 h after the LPS challenge. The level of inflammatory cytokine (tumor necrosis factor-α) was elevated at 2 h, which was reduced significantly in CLD + MacC21 + LPS-treated animals. Also, CLD + MacC21 + LPS-treated animals had elevated plasma and renal IL-10, indicating an anti-inflammatory role of C21-treated BMDMs. Renal functional injury in CLD + MacC21 + LPS-treated animals was partially improved. Collectively, the data demonstrate that BMDM AT2R stimulation results in anti-inflammation and partial renoprotection against early stages of LPS-induced AKI.NEW & NOTEWORTHY Endotoxin such as lipopolysaccharide (LPS) induces acute kidney injury (AKI), which is a risk factor for and often leads to chronic kidney diseases. The present study revealed that bone marrow-derived macrophage activation of the angiotensin II type 2 receptor (AT2R) contributes to the anti-inflammation and partial renoprotection against early stages of LPS-induced AKI. Since AT2R is an emerging anti-inflammatory and organ-protective target, this study advances our understanding of AT2R's anti-inflammatory mechanisms associated with renoprotection.

Investigating the renoprotective effect of C21 in male mice with sepsis via modulation of p-AKT/PI3K expression

This study aimed to investigate if C21 could prevent acute renal injury induced by sepsis by regulating the expression of p-AKT/PI3K. Five equal groups of 25 adult male Swiss-albino mice were randomly divided (n=5): sham (laparotomy without CLP), CLP, vehicle (equivalent amount of DMSO one hour before CLP), and C21 (0.03 mg/kg, one hour before CLP). ELISA was used to measure serum inflammatory mediators, and the expression of PI3K and P-AKT was determined using PCR and immunohistochemistry (IHC), respectively. TNF, TNF receptor, F8-isoprostane, urea, creatinine, and IL-6 blood levels were considerably lower in the CLP group (p<0.05) compared to the sham group, whereas the C21 treated group had significantly (p<0.05) greater levels of these inflammatory mediators. The IHC analysis revealed that P-AKT expression was significantly lower (p<0.05) in the CLP group compared to the sham group, while the C21 pretreatment group had significantly higher levels of P-AKT expression compared to the CLP group (p<0.05). The PI3K expression in the CLP group was significantly lower than in the sham group (p<0.05), according to PCR results, whereas the PI3K expression in the C21 pretreatment group was significantly greater than in the CLP group (p<0.05). This study showed that C21 might reduce levels of pro-inflammatory cytokines, including TNF-, IL-6, and TNF receptor, by modulating the PI3K/AKT signaling pathways, which can, in turn, reduce renal dysfunction during CLP-induced sepsis in male mice.

The Novel AT2 Receptor Agonist β-Pro7-AngIII Exerts Cardiac and Renal Anti-Fibrotic and Anti-Inflammatory Effects in High Salt-Fed Mice

A high salt (HS) diet is associated with an increased risk for cardiovascular diseases (CVDs) and fibrosis is a key contributor to the organ dysfunction involved in CVDs. The activation of the renin angiotensin type 2 receptor (AT₂R) has been considered as organ protective in many CVDs. However, there are limited AT₂R-selective agonists available. Our first reported β-substituted angiotensin III peptide, β-Pro⁷-AngIII, showed high selectivity for the AT₂R. In the current study, we examine the potential anti-fibrotic and anti-inflammatory effects of this novel AT₂R-selective peptide on HS-induced organ damage. FVB/N mice fed with a 5% HS diet for 8 weeks developed cardiac and renal fibrosis and inflammation, which were associated with increased TGF-β1 levels in heart, kidney and plasma. Four weeks' treatment (from weeks 5-8) with β-Pro⁷-AngIII inhibited the HS-induced cardiac and renal fibrosis and inflammation. These protective effects were accompanied by reduced local and systemic TGF-β1 as well as reduced cardiac myofibroblast differentiation. Importantly, the anti-fibrotic and anti-inflammatory effects caused by β-Pro⁷-AngIII were attenuated by the AT₂R antagonist PD123319. These results demonstrate, for the first time, the cardio- and reno-protective roles of the AT₂R-selective β-Pro⁷-AngIII, highlighting it as an important therapeutic that can target the AT₂R to treat end-organ damage.

Protecting glomerulus: role of angiotensin-II type 2 receptor

Podocyte injury due to either drug, toxin, infection, or metabolic abnormality is a great concern as it increases the risk of developing focal segmental glomerulosclerosis (FSGS) and proteinuric kidney diseases. The direct podocyte injury due to doxorubicin is associated with an increase in proinflammatory cytokines and induction of cathepsin L. The increased activity of cathepsin L in turn may degrade the glomerular slit diaphragm resulting in proteinuric kidney injury. The angiotensin-II type 2 receptor (AT2R) has earlier been reported to be associated with the preservation of slit diaphragm proteins and prevention of proteinuria. Recent in vivo findings by Zhang and colleagues further support the anti-proteinuric role of AT2R in preventing podocyte injury via down-regulating cytokines ccl2, and hence, cathepsin L, thereby, limiting the progression of FSGS.

Double-Negative T Cells Attenuate Cisplatin-Induced Acute Kidney Injury via Upregulating IL-10/AT2R Axis

Objective

Our previous research showed that TCR+CD4-CD8-double-negative (DN) T cells protect renal epithelial cells from cisplatin-induced acute kidney injury (AKI). Therefore, this study is aimed at investigating the mechanism underlying the effect of DN T cells against Cis-induced AKI.

Methods

HK-2 cells cultured alone or with DN T cells were treated with or without Cis. After treatment, the cell viability and death were analyzed by a CCK-8 kit and flow cytometric assay with Annexin V/PI staining, respectively. The expressions of inflammatory factors in HK-2 and DN T cells were analyzed using qPCR. The expression levels of nephrotoxicity-associated biomarkers (KIM, calbindin, and TIMP-1), Bcl-2, and angiotensin AT2 receptor (AT2R) were determined by Western blot and qPCR.

Results

The administration of cisplatin significantly decreased the cell viability and AT2R expression, and increased cell death, inflammatory factors, and nephrotoxicity-associated biomarkers of HK-2 cells, while these effects were partly attenuated when cocultured with DN T cells. IL-10 expression was significantly increased in DN T cells after coculture, and cisplatin treatment aggravated this elevation. IL-10 supplementation exhibited a similar effect to coculture, whereas anti-IL-10 antibody reversed the effect of coculture on cisplatin-treated HK-2 cells. Finally, PD123319, an AT2R antagonist, also reversed the effect of IL-10 and coculture on the cell viability, death, and the expression of KIM, calbindin, TIMP-1, and Bcl-2 of cisplatin-treated HK-2 cells.

Conclusions

DN T cells protected HK-2 cells from cisplatin-induced injury through IL-10/AT2R axis, which may act as a potential target for the treatment of cisplatin-induced AKI.

Tripeptide IRW Protects MC3T3-E1 Cells against Ang II Stress in an AT2R Dependent Manner

Multiple strategies including the use of bioactive peptides and other nutraceuticals are being adopted to maintain bone health. This study provides an improved and deeper understanding of the pharmacological effects that a bioactive peptide IRW (Ile-Arg-Trp) extends on bone health. Our results showed that IRW treatment protects osteoblasts against Ang II induced decline in cell proliferation and restores protein levels of collagen type I alpha 2 chain (COL1A2) and alkaline phosphatase (ALP) levels in MC3T3-E1 cells (p < 0.05). Apart from augmentation of these mineralization factors, the angiotensin II (Ang II) induced apoptotic stress in osteoblasts was mitigated by IRW as well. At the molecular level, IRW abolished the cytochrome-c release via modulation of pro-and anti-apoptotic genes in MC3T3-E1 cells (p < 0.05). Interestingly, IRW also increased cellular levels of cytoprotective local RAAS factors such as MasR, Ang (1−7), ACE2, and AT2R, and lowered the levels of Ang II effector receptor (AT1R). Further, our results indicated a lower content of inflammation and osteoclastogenesis biomarkers such as cyclooxygenase 2 (COX2), nuclear factor kappa B (NF-κB), and receptor activator of nuclear factor kappa-B ligand (RANKL) following IRW treatment in MC3T3-E1 cells (p < 0.05). The use of an antagonist-guided cell study indicated that IRW contributed to the process of cytoprotection and proliferation of osteoblasts via Runt-related transcription factor 2 (RUNX2) in face of Ang II stress in an AT2R dependent manner. The key findings of our study showed that IRW could potentially have a therapeutic role in the treatment and/or prevention of bone disorders.

Angiotensin type 2 receptor activation limits kidney injury during the early phase and induces Treg cells during the late phase of renal ischemia

Kidney infiltrating immune cells such as monocytes, neutrophils, and T cells play critical roles in renal ischemia-reperfusion (IR) injury and repair. Recently, the angiotensin II type 2 receptor (AT2R) has been implicated in protecting kidneys against injury and monocyte infiltration, particularly in chronic kidney disease. However, the role of AT2R in IR injury and repair phases and T cell modulation is unknown. To address this question, Sprague-Dawley rats were subjected to IR with or without AT2R agonist C21 treatment. IR caused early (2 h postreperfusion) renal functional injury (proteinuria, plasma urea, and creatinine) and enhanced immune cells (T cells and CD4 T cells) infiltration and levels of the proinflammatory cytokines monocyte chemoattractant protein-1, TNF-α, and IL-6. C21 treatment reversed these changes but increased the anti-inflammatory IL-10 level. On day 3, C21 treatment increased CD4+FoxP3+ (regulatory T cells) and CD4+IL-10+ cells and reduced kidney injury molecule-1 and neutrophil gelatinase-associated lipocalin in the kidney compared with the IR control, suggesting the involvement of AT2R in kidney repair. These data indicate that AT2R activation protects the kidney against IR injury and immune cell infiltration in the early phase and modulates CD4 T cells toward the regulatory T cell phenotype, which may have long-term beneficial effects on kidney function.NEW & NOTEWORTHY The angiotensin II type 2 receptor agonist C21 has been known to have a renoprotective role in various kidney pathologies. C21 treatment (before renal ischemia) attenuated postischemic kidney injury, kidney dysfunction, and immune cell infiltration during the injury phase. Also, C21 treatment modulated the kidney microenvironment by enhancing anti-inflammatory responses mainly mediated by IL-10. During the repair phase, C21 treatment enhanced IL-10-secreting CD4 T cells and FoxP3-secreting regulatory T cells in Sprague-Dawley rats.

Angiotensin AT2 Receptor is Anti-inflammatory and Reno-Protective in Lipopolysaccharide Mice Model: Role of IL-10

Acute kidney injury (AKI) due to endotoxemic insult is predicted by the infiltration of neutrophils, monocytes and macrophages, and the release of pro-and anti-inflammatory cytokines to the site of injury. Earlier, we have demonstrated the role of angiotensin-II type 2 receptor (AT2R) stimulation in reno-protection in lipopolysaccharide (LPS)-induced inflammation and AKI in C57BL6/NHsd mice. Moreover, AT2R activation has been shown to increase the anti-inflammatory cytokine interleukin-10 (IL-10), its role in AT2R-mediated anti-inflammation and reno-protection is unknown. To address this question, in the present study mice were treated with the AT2R agonist C21 (0.3 mg/kg, intraperitoneally), LPS (5 mg/kg, intraperitoneally), or LPS with C21 pre-treatment with or without neutralizing IL-10 antibody. Treatment with C21 alone caused an increase in the plasma and kidney IL-10 levels, which peaks at 2-h, and returned to baseline at 6-h. The C21-induced IL-10 increase was blocked by the AT2R antagonist PD123319 suggesting AT2R's involvement. LPS treatment caused a profound increase in tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) and the LPS-induced increase in these cytokines was attenuated by the C21 pre-treatment (1-h prior LPS) both in the plasma and kidney. Neutralizing IL-10 antibody treatment abrogated the C21-lowering of TNF-α and IL-6 in the kidney but not in the plasma. Similar results as related to the cytokines profiles in all the groups were also observed in the heart and spleen. The alteration in early cytokine profile prompted us to measure the markers of renal function (blood urea nitogen and urinary creatinine) in order to analyze the effect of IL-10 neutralization. However, it was too early to observe changes in renal function. Therefore, the renal function and injury markers were again measured at 24 h. Treatment with neutralizing IL-10 antibody attenuated the C21-mediated improvement in indices of the kidney function, but not the biomarkers of renal injury (kidney injury molecule-1 and neutrophil-gelatinase associated lipocalin). Collectively, our data suggest that the involvement of IL-10 in AT2R-mediated anti-inflammation and reno-protection against LPS is complex, mediating the renal cytokine profile and kidney filtration function, but not the plasma cytokine profile and renal injury markers.

Angiotensin II Type 2 Receptor: A Target for Protection Against Hypertension, Metabolic Dysfunction, and Organ Remodeling

The renin-angiotensin system is of vital significance not only in the maintenance of blood pressure but also because of its role in the pathophysiology of different organ systems in the body. Of the 2 Ang II (angiotensin II) receptors, the AT₁R (Ang II type 1 receptor) has been extensively studied for its role in mediating the classical functions of Ang II, including vasoconstriction, stimulation of renal tubular sodium reabsorption, hormonal secretion, cell proliferation, inflammation, and oxidative stress. The other receptor, AT₂R (Ang II type 2 receptor), is abundantly expressed in both immune and nonimmune cells in fetal tissue. However, its expression is increased under pathological conditions in adult tissues. The role of AT₂R in counteracting AT₁R function has been discussed in the past 2 decades. However, with the discovery of the nonpeptide agonist C21, the significance of AT₂R in various pathologies such as obesity, hypertension, and kidney diseases have been examined. This review focuses on the most recent findings on the beneficial effects of AT₂R by summarizing both gene knockout studies as well as pharmacological studies, specifically highlighting its importance in blood pressure regulation, obesity/metabolism, organ protection, and relevance in the treatment of coronavirus disease 2019 (COVID-19).

Angiotensin (1-7) Attenuates Sepsis-Induced Acute Kidney Injury by Regulating the NF-κB Pathway

This study explores the protective mechanism of angiotensin (1-7) [Ang-(1-7)] on kidneys by examining its effects on renal histomorphology, inflammatory response, oxidative stress, and NF-κB signaling in mice suffering from sepsis-induced acute kidney injury. A sepsis-induced acute kidney injury mouse model was established by intracervically injecting lipopolysaccharides (LPS group), followed by the administration of Ang-(1-7) [LPS + Ang-(1-7) group]. The serum levels of urea nitrogen, creatinine and cystatin. c were measured with an automatic biochemical analyzer, and changes in proinflammatory cytokines and angiotensin II (Ang II) in the serum and kidneys were quantified by enzyme-linked immunosorbent assays. Changes in oxidative stress indices in the renal cortex were detected by colorimetry. The localization of Ang II in kidneys was examined by immunohistochemistry. Western blotting was used to examine phosphorylated NF-κB-p65 and IκBα levels in kidneys. Compared with the control group, the serum levels of urea nitrogen, creatinine and cystatin. c were increased, whereas the levels of Ang II, TNFα, IL-1β, IL-6, and malondialdehyde (mda) were increased significantly. The levels of Ang II and phosphorylated NF-κB-p65 were elevated in kidneys, whereas the levels of superoxide dismutase (sod), Total antioxidative capacity (TAOC), and inhibitor of NF-κB (IκBα) were reduced in the LPS group (p < 0.05). Pathological damage was also observed in kidneys of LPS-group mice. In Pearson correlation analysis, there was a positive correlation between Ang II and phosphorylated NF-κB-p65 levels, and a negative correlation between Ang II and IκBα levels (p < 0.05). After the application of Ang-(1-7), the levels of urea nitrogen, creatinine, cystatin. c, Ang II, TNFα, IL-1β, IL-6, and mda, as well as the expression of Ang II and phosphorylated NF-κB-p65 in kidneys of LPS + Ang-(1-7)-group mice, were lower than those in kidneys of LPS-group mice, but the levels of sod, TAOC, and IκBα were higher than those of LPS-group mice (p < 0.05). Pathological changes were less severe in mice of the LPS + Ang-(1-7) group. Overall, Ang-(1-7) can decrease the Ang II level, inhibit NF-κB signaling, reduce the inflammatory response, decrease oxidative stress, and mitigate sepsis-associated acute kidney injury.

Emerging Role of Angiotensin AT2 Receptor in Anti-Inflammation: An Update

The hyperactive RAS and inflammation are closely associated. The angiotensin-II/AT1R axis of the RAS has been explored extensively for its role in inflammation and a plethora of pathological conditions. Understanding the role of AT2R in inflammation is an emerging area of research. The AT2R is expressed on a variety of immune and non-immune cells, which upon activation triggers the release of a host of cytokines and has multiple effects that coalesce to anti-inflammation and prevents maladaptive repair. The anti-inflammatory outcomes of AT2R activation are linked to its well-established signaling pathways involving formation of nitric oxide and activation of phosphatases. Collectively, these effects promote cell survival and tissue function. The consideration of AT2R as a therapeutic target requires further investigations.